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diff --git a/chromium/third_party/blink/renderer/core/frame/sticky_frame_tracker.h b/chromium/third_party/blink/renderer/core/frame/sticky_frame_tracker.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_FRAME_STICKY_FRAME_TRACKER_H_
+#define THIRD_PARTY_BLINK_RENDERER_CORE_FRAME_STICKY_FRAME_TRACKER_H_
+
+#include "third_party/blink/renderer/core/core_export.h"
+#include "third_party/blink/renderer/platform/geometry/int_point.h"
+#include "third_party/blink/renderer/platform/wtf/deque.h"
+
+namespace blink {
+
+// Keeps track of the viewport position of a frame.
+//
+// This is for catching ads that don't follow the Better Ads Standard --
+// https://www.betterads.org/desktop-large-sticky-ad/.
+//
+// The heuristic for "sticky" is as follows:
+//
+// Given the latest two pairs of main frame scroll offset and frame's position
+// wrt viewport (a.k.a. viewport offset), if the two main frame scroll offsets
+// differ while the viewport offsets are the same, the frame is considered
+// sticky.
+//
+// In addition, we store the latest 10 (|kNumScrollEvents|) main frame scroll
+// offsets and viewport offsets, and keep comparing their range. For the latest
+// 10 recordings, if the frame has a viewport offsets range smaller than 0.5
+// (|kStickyFrameOffsetsRangeToScrollOffsetsRangeThreshold|) of the main frame
+// scroll offsets range, then it's considered sticky as well.
+//
+// Right now we only consider offsets on the vertical dimension. The
+// implementation can be extended to cover both dimensions if needed.
+class CORE_EXPORT StickyFrameTracker {
+ public:
+  // Returns whether the |frame_size| is considered large compared to
+  // |main_frame_viewport_size|.
+  static bool IsLarge(const IntSize& main_frame_viewport_size,
+                      const IntSize& frame_size);
+
+  StickyFrameTracker() = default;
+  StickyFrameTracker(const StickyFrameTracker&) = delete;
+  ~StickyFrameTracker() = default;
+
+  // Called when the frame's position with respect to the viewport may have
+  // changed. Returns whether the frame is sticky. |main_frame_scroll_offset|
+  // is the scroll position in the main page. |viewport_offset| is the position
+  // of the top-left corner of this frame (every StickyFrameTracker will only be
+  // tracking one frame) relative to the browser viewport.
+  bool UpdateStickyStatus(const IntPoint& main_frame_scroll_offset,
+                          const IntPoint& viewport_offset);
+
+ private:
+  void SetSticky();
+
+  bool is_sticky_ = false;
+  Deque<int> viewport_offsets_;
+  Deque<int> main_frame_scroll_offsets_;
+};
+
+}  // namespace blink
+
+#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_FRAME_STICKY_FRAME_TRACKER_H_