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diff --git a/chromium/third_party/blink/renderer/core/layout/jank_region.h b/chromium/third_party/blink/renderer/core/layout/jank_region.h
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+++ b/chromium/third_party/blink/renderer/core/layout/jank_region.h
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+// Copyright 2018 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_LAYOUT_JANK_REGION_H_
+#define THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_JANK_REGION_H_
+
+#include "third_party/blink/renderer/core/core_export.h"
+#include "third_party/blink/renderer/platform/geometry/int_rect.h"
+#include "third_party/blink/renderer/platform/wtf/vector.h"
+
+namespace blink {
+
+// Represents a per-frame jank region for JankTracker. Only used when the
+// JankTrackingSweepLine feature is enabled.
+//
+// This class uses a sweep line algorithm to compute the area in O(n log n) time
+// where n is the number of rects recorded by AddRect. For complex jank regions,
+// this is more efficient than using blink::Region, which is worst-case O(n^2)
+// from the repeated calls to Region::Unite.
+//
+// The high-level approach is described here:
+// http://jeffe.cs.illinois.edu/open/klee.html
+//
+// The sweep line moves from left to right. (TODO: compare performance against a
+// top-to-bottom sweep.)
+//
+// The sweep line's current intersection with the jank region ("active length")
+// is tracked by a segment tree, similar to what is described at:
+// https://en.wikipedia.org/wiki/Segment_tree
+//
+// There are some subtleties to the segment tree, which are described by the
+// comments in the implementation.
+
+class CORE_EXPORT JankRegion {
+ public:
+  void AddRect(const IntRect& rect) {
+    if (!rect.IsEmpty())
+      rects_.push_back(rect);
+  }
+
+  const Vector<IntRect>& GetRects() const { return rects_; }
+  bool IsEmpty() const { return rects_.IsEmpty(); }
+  void Reset() { rects_.clear(); }
+
+  uint64_t Area() const;
+
+ private:
+  Vector<IntRect> rects_;
+};
+
+}  // namespace blink
+
+#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_JANK_REGION_H_