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diff --git a/Source/JavaScriptCore/heap/HeapSnapshotBuilder.cpp b/Source/JavaScriptCore/heap/HeapSnapshotBuilder.cpp
new file mode 100644
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+++ b/Source/JavaScriptCore/heap/HeapSnapshotBuilder.cpp
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+/*
+ * Copyright (C) 2016 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+ */
+
+#include "config.h"
+#include "HeapSnapshotBuilder.h"
+
+#include "DeferGC.h"
+#include "Heap.h"
+#include "HeapProfiler.h"
+#include "HeapSnapshot.h"
+#include "JSCInlines.h"
+#include "JSCell.h"
+#include "PreventCollectionScope.h"
+#include "VM.h"
+#include <wtf/text/StringBuilder.h>
+
+namespace JSC {
+    
+unsigned HeapSnapshotBuilder::nextAvailableObjectIdentifier = 1;
+unsigned HeapSnapshotBuilder::getNextObjectIdentifier() { return nextAvailableObjectIdentifier++; }
+void HeapSnapshotBuilder::resetNextAvailableObjectIdentifier() { HeapSnapshotBuilder::nextAvailableObjectIdentifier = 1; }
+
+HeapSnapshotBuilder::HeapSnapshotBuilder(HeapProfiler& profiler)
+    : m_profiler(profiler)
+{
+}
+
+HeapSnapshotBuilder::~HeapSnapshotBuilder()
+{
+}
+
+void HeapSnapshotBuilder::buildSnapshot()
+{
+    PreventCollectionScope preventCollectionScope(m_profiler.vm().heap);
+    
+    m_snapshot = std::make_unique<HeapSnapshot>(m_profiler.mostRecentSnapshot());
+    {
+        m_profiler.setActiveSnapshotBuilder(this);
+        m_profiler.vm().heap.collectAllGarbage();
+        m_profiler.setActiveSnapshotBuilder(nullptr);
+    }
+    m_snapshot->finalize();
+
+    m_profiler.appendSnapshot(WTFMove(m_snapshot));
+}
+
+void HeapSnapshotBuilder::appendNode(JSCell* cell)
+{
+    ASSERT(m_profiler.activeSnapshotBuilder() == this);
+    ASSERT(Heap::isMarkedConcurrently(cell));
+
+    if (hasExistingNodeForCell(cell))
+        return;
+
+    std::lock_guard<Lock> lock(m_buildingNodeMutex);
+
+    m_snapshot->appendNode(HeapSnapshotNode(cell, getNextObjectIdentifier()));
+}
+
+void HeapSnapshotBuilder::appendEdge(JSCell* from, JSCell* to)
+{
+    ASSERT(m_profiler.activeSnapshotBuilder() == this);
+    ASSERT(to);
+
+    // Avoid trivial edges.
+    if (from == to)
+        return;
+
+    std::lock_guard<Lock> lock(m_buildingEdgeMutex);
+
+    m_edges.append(HeapSnapshotEdge(from, to));
+}
+
+void HeapSnapshotBuilder::appendPropertyNameEdge(JSCell* from, JSCell* to, UniquedStringImpl* propertyName)
+{
+    ASSERT(m_profiler.activeSnapshotBuilder() == this);
+    ASSERT(to);
+
+    std::lock_guard<Lock> lock(m_buildingEdgeMutex);
+
+    m_edges.append(HeapSnapshotEdge(from, to, EdgeType::Property, propertyName));
+}
+
+void HeapSnapshotBuilder::appendVariableNameEdge(JSCell* from, JSCell* to, UniquedStringImpl* variableName)
+{
+    ASSERT(m_profiler.activeSnapshotBuilder() == this);
+    ASSERT(to);
+
+    std::lock_guard<Lock> lock(m_buildingEdgeMutex);
+
+    m_edges.append(HeapSnapshotEdge(from, to, EdgeType::Variable, variableName));
+}
+
+void HeapSnapshotBuilder::appendIndexEdge(JSCell* from, JSCell* to, uint32_t index)
+{
+    ASSERT(m_profiler.activeSnapshotBuilder() == this);
+    ASSERT(to);
+
+    std::lock_guard<Lock> lock(m_buildingEdgeMutex);
+
+    m_edges.append(HeapSnapshotEdge(from, to, index));
+}
+
+bool HeapSnapshotBuilder::hasExistingNodeForCell(JSCell* cell)
+{
+    if (!m_snapshot->previous())
+        return false;
+
+    return !!m_snapshot->previous()->nodeForCell(cell);
+}
+
+
+// Heap Snapshot JSON Format:
+//
+//   {
+//      "version": 1.0,
+//      "nodes": [
+//          <nodeId>, <sizeInBytes>, <nodeClassNameIndex>, <internal>,
+//          <nodeId>, <sizeInBytes>, <nodeClassNameIndex>, <internal>,
+//          ...
+//      ],
+//      "nodeClassNames": [
+//          "string", "Structure", "Object", ...
+//      ],
+//      "edges": [
+//          <fromNodeId>, <toNodeId>, <edgeTypeIndex>, <edgeExtraData>,
+//          <fromNodeId>, <toNodeId>, <edgeTypeIndex>, <edgeExtraData>,
+//          ...
+//      ],
+//      "edgeTypes": [
+//          "Internal", "Property", "Index", "Variable"
+//      ],
+//      "edgeNames": [
+//          "propertyName", "variableName", ...
+//      ]
+//   }
+//
+// Notes:
+//
+//     <nodeClassNameIndex>
+//       - index into the "nodeClassNames" list.
+//
+//     <internal>
+//       - 0 = false, 1 = true.
+//
+//     <edgeTypeIndex>
+//       - index into the "edgeTypes" list.
+//
+//     <edgeExtraData>
+//       - for Internal edges this should be ignored (0).
+//       - for Index edges this is the index value.
+//       - for Property or Variable edges this is an index into the "edgeNames" list.
+
+static uint8_t edgeTypeToNumber(EdgeType type)
+{
+    return static_cast<uint8_t>(type);
+}
+
+static const char* edgeTypeToString(EdgeType type)
+{
+    switch (type) {
+    case EdgeType::Internal:
+        return "Internal";
+    case EdgeType::Property:
+        return "Property";
+    case EdgeType::Index:
+        return "Index";
+    case EdgeType::Variable:
+        return "Variable";
+    }
+    ASSERT_NOT_REACHED();
+    return "Internal";
+}
+
+String HeapSnapshotBuilder::json()
+{
+    return json([] (const HeapSnapshotNode&) { return true; });
+}
+
+String HeapSnapshotBuilder::json(std::function<bool (const HeapSnapshotNode&)> allowNodeCallback)
+{
+    VM& vm = m_profiler.vm();
+    DeferGCForAWhile deferGC(vm.heap);
+
+    // Build a node to identifier map of allowed nodes to use when serializing edges.
+    HashMap<JSCell*, unsigned> allowedNodeIdentifiers;
+
+    // Build a list of used class names.
+    HashMap<const char*, unsigned> classNameIndexes;
+    classNameIndexes.set("<root>", 0);
+    unsigned nextClassNameIndex = 1;
+
+    // Build a list of used edge names.
+    HashMap<UniquedStringImpl*, unsigned> edgeNameIndexes;
+    unsigned nextEdgeNameIndex = 0;
+
+    StringBuilder json;
+
+    auto appendNodeJSON = [&] (const HeapSnapshotNode& node) {
+        // Let the client decide if they want to allow or disallow certain nodes.
+        if (!allowNodeCallback(node))
+            return;
+
+        allowedNodeIdentifiers.set(node.cell, node.identifier);
+
+        auto result = classNameIndexes.add(node.cell->classInfo(vm)->className, nextClassNameIndex);
+        if (result.isNewEntry)
+            nextClassNameIndex++;
+        unsigned classNameIndex = result.iterator->value;
+
+        bool isInternal = false;
+        if (!node.cell->isString()) {
+            Structure* structure = node.cell->structure(vm);
+            isInternal = !structure || !structure->globalObject();
+        }
+
+        // <nodeId>, <sizeInBytes>, <className>, <optionalInternalBoolean>
+        json.append(',');
+        json.appendNumber(node.identifier);
+        json.append(',');
+        json.appendNumber(node.cell->estimatedSizeInBytes());
+        json.append(',');
+        json.appendNumber(classNameIndex);
+        json.append(',');
+        json.append(isInternal ? '1' : '0');
+    };
+
+    bool firstEdge = true;
+    auto appendEdgeJSON = [&] (const HeapSnapshotEdge& edge) {
+        if (!firstEdge)
+            json.append(',');
+        firstEdge = false;
+
+        // <fromNodeId>, <toNodeId>, <edgeTypeIndex>, <edgeExtraData>
+        json.appendNumber(edge.from.identifier);
+        json.append(',');
+        json.appendNumber(edge.to.identifier);
+        json.append(',');
+        json.appendNumber(edgeTypeToNumber(edge.type));
+        json.append(',');
+        switch (edge.type) {
+        case EdgeType::Property:
+        case EdgeType::Variable: {
+            auto result = edgeNameIndexes.add(edge.u.name, nextEdgeNameIndex);
+            if (result.isNewEntry)
+                nextEdgeNameIndex++;
+            unsigned edgeNameIndex = result.iterator->value;
+            json.appendNumber(edgeNameIndex);
+            break;
+        }
+        case EdgeType::Index:
+            json.appendNumber(edge.u.index);
+            break;
+        default:
+            // No data for this edge type.
+            json.append('0');
+            break;
+        }
+    };
+
+    json.append('{');
+
+    // version
+    json.appendLiteral("\"version\":1");
+
+    // nodes
+    json.append(',');
+    json.appendLiteral("\"nodes\":");
+    json.append('[');
+    json.appendLiteral("0,0,0,0"); // <root>
+    for (HeapSnapshot* snapshot = m_profiler.mostRecentSnapshot(); snapshot; snapshot = snapshot->previous()) {
+        for (auto& node : snapshot->m_nodes)
+            appendNodeJSON(node);
+    }
+    json.append(']');
+
+    // node class names
+    json.append(',');
+    json.appendLiteral("\"nodeClassNames\":");
+    json.append('[');
+    Vector<const char *> orderedClassNames(classNameIndexes.size());
+    for (auto& entry : classNameIndexes)
+        orderedClassNames[entry.value] = entry.key;
+    classNameIndexes.clear();
+    bool firstClassName = true;
+    for (auto& className : orderedClassNames) {
+        if (!firstClassName)
+            json.append(',');
+        firstClassName = false;
+        json.appendQuotedJSONString(className);
+    }
+    orderedClassNames.clear();
+    json.append(']');
+
+    // Process edges.
+    // Replace pointers with identifiers.
+    // Remove any edges that we won't need.
+    m_edges.removeAllMatching([&] (HeapSnapshotEdge& edge) {
+        // If the from cell is null, this means a <root> edge.
+        if (!edge.from.cell)
+            edge.from.identifier = 0;
+        else {
+            auto fromLookup = allowedNodeIdentifiers.find(edge.from.cell);
+            if (fromLookup == allowedNodeIdentifiers.end())
+                return true;
+            edge.from.identifier = fromLookup->value;
+        }
+
+        if (!edge.to.cell)
+            edge.to.identifier = 0;
+        else {
+            auto toLookup = allowedNodeIdentifiers.find(edge.to.cell);
+            if (toLookup == allowedNodeIdentifiers.end())
+                return true;
+            edge.to.identifier = toLookup->value;
+        }
+
+        return false;
+    });
+    allowedNodeIdentifiers.clear();
+    m_edges.shrinkToFit();
+
+    // Sort edges based on from identifier.
+    std::sort(m_edges.begin(), m_edges.end(), [&] (const HeapSnapshotEdge& a, const HeapSnapshotEdge& b) {
+        return a.from.identifier < b.from.identifier;
+    });
+
+    // edges
+    json.append(',');
+    json.appendLiteral("\"edges\":");
+    json.append('[');
+    for (auto& edge : m_edges)
+        appendEdgeJSON(edge);
+    json.append(']');
+
+    // edge types
+    json.append(',');
+    json.appendLiteral("\"edgeTypes\":");
+    json.append('[');
+    json.appendQuotedJSONString(edgeTypeToString(EdgeType::Internal));
+    json.append(',');
+    json.appendQuotedJSONString(edgeTypeToString(EdgeType::Property));
+    json.append(',');
+    json.appendQuotedJSONString(edgeTypeToString(EdgeType::Index));
+    json.append(',');
+    json.appendQuotedJSONString(edgeTypeToString(EdgeType::Variable));
+    json.append(']');
+
+    // edge names
+    json.append(',');
+    json.appendLiteral("\"edgeNames\":");
+    json.append('[');
+    Vector<UniquedStringImpl*> orderedEdgeNames(edgeNameIndexes.size());
+    for (auto& entry : edgeNameIndexes)
+        orderedEdgeNames[entry.value] = entry.key;
+    edgeNameIndexes.clear();
+    bool firstEdgeName = true;
+    for (auto& edgeName : orderedEdgeNames) {
+        if (!firstEdgeName)
+            json.append(',');
+        firstEdgeName = false;
+        json.appendQuotedJSONString(edgeName);
+    }
+    orderedEdgeNames.clear();
+    json.append(']');
+
+    json.append('}');
+    return json.toString();
+}
+
+} // namespace JSC