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diff --git a/chromium/third_party/blink/renderer/core/css/resolver/cascade_map.h b/chromium/third_party/blink/renderer/core/css/resolver/cascade_map.h
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+++ b/chromium/third_party/blink/renderer/core/css/resolver/cascade_map.h
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+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_CSS_RESOLVER_CASCADE_MAP_H_
+#define THIRD_PARTY_BLINK_RENDERER_CORE_CSS_RESOLVER_CASCADE_MAP_H_
+
+#include <bitset>
+#include "third_party/blink/renderer/core/css/css_property_name.h"
+#include "third_party/blink/renderer/core/css/css_property_names.h"
+#include "third_party/blink/renderer/core/css/resolver/cascade_priority.h"
+#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
+
+namespace blink {
+
+// Optimized map from CSSPropertyNames to CascadePriority.
+//
+// Because using a HashMap for everything is quite expensive in terms of
+// performance, this class stores standard (non-custom) properties in a fixed-
+// size array, and only custom properties are stored in a HashMap.
+class CORE_EXPORT CascadeMap {
+  STACK_ALLOCATED();
+
+ public:
+  // Get the CascadePriority for the given CSSPropertyName. If there is no
+  // entry for the given name, CascadePriority() is returned.
+  CascadePriority At(const CSSPropertyName&) const;
+  // Find the CascadePriority location for a given name, if present. If there
+  // is no entry for the given name, nullptr is returned.
+  //
+  // Note that the returned pointer may accessed to change the stored value.
+  //
+  // Note also that calling Add() invalidates the pointer.
+  CascadePriority* Find(const CSSPropertyName&);
+  // Adds an an entry to the map if the incoming priority is greater than or
+  // equal to the current priority for the same name.
+  void Add(const CSSPropertyName&, CascadePriority);
+  // Added properties with CSSPropertyPriority::kHighPropertyPriority cause the
+  // corresponding high_priority_-bit to be set. This provides a fast way to
+  // check which high-priority properties have been added (if any).
+  uint64_t HighPriorityBits() const { return high_priority_; }
+  // Remove all properties (both native and custom) from the CascadeMap.
+  void Reset();
+
+ private:
+  uint64_t high_priority_ = 0;
+  // For performance reasons, a char-array is used to prevent construction of
+  // CascadePriority objects. A companion std::bitset keeps track of which
+  // properties are initialized.
+  std::bitset<numCSSProperties> native_property_bits_;
+  alignas(CascadePriority) char native_properties_[numCSSProperties *
+                                                   sizeof(CascadePriority)];
+  HashMap<CSSPropertyName, CascadePriority> custom_properties_;
+};
+
+}  // namespace blink
+
+#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_CSS_RESOLVER_CASCADE_MAP_H_