Prevent overlay scrollbars expand or hover together

cc/input/single_scrollbar_animation_controller_thinning.h

Index: cc/input/single_scrollbar_animation_controller_thinning.h
diff --git a/cc/input/single_scrollbar_animation_controller_thinning.h b/cc/input/single_scrollbar_animation_controller_thinning.h
new file mode 100644
index 0000000000000000000000000000000000000000..a240e911e95a608c909f286acdf490df4fa060c0
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+++ b/cc/input/single_scrollbar_animation_controller_thinning.h
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+// Copyright 2013 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 CC_INPUT_SINGLE_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_
+#define CC_INPUT_SINGLE_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/time/time.h"
+#include "cc/base/cc_export.h"
+#include "cc/input/scrollbar_animation_controller.h"
+#include "cc/layers/layer_impl.h"
+#include "cc/layers/scrollbar_layer_impl_base.h"
+#include "ui/gfx/geometry/vector2d_f.h"
+
+namespace cc {
+
+// ScrollbarAnimationControllerThinning for one scrollbar
+class CC_EXPORT SingleScrollbarAnimationControllerThinning {
+ public:
+  static std::unique_ptr<SingleScrollbarAnimationControllerThinning> Create(
+      int scroll_layer_id,
+      ScrollbarOrientation orientation,
+      ScrollbarAnimationControllerClient* client,
+      base::CancelableClosure* delayed_scrollbar_fade,
+      base::TimeDelta thinning_duration);
+
+  ~SingleScrollbarAnimationControllerThinning() {}
+
+  void set_mouse_move_distance_for_test(float distance) {
+    mouse_move_distance_to_trigger_animation_ = distance;
+  }
+  bool mouse_is_over_scrollbar() const { return mouse_is_over_scrollbar_; }
+  bool mouse_is_near_scrollbar() const { return mouse_is_near_scrollbar_; }
+  bool captured() const { return captured_; }
+
+  bool Animate(base::TimeTicks now);
+  void StartAnimation();
+  void StopAnimation();
+
+  bool ShouldFadeOut() const;
+  void UpdateThumbThicknessScale();
+
+  void DidMouseDown();
+  void DidMouseUp();
+  void DidMouseLeave();
+  void DidMouseMoveNear(float distance);
+
+  bool Hidden() const { return hidden_; }
+  void SetHidden(bool hidden) { hidden_ = hidden; }
+
+ private:
+  SingleScrollbarAnimationControllerThinning(
+      int scroll_layer_id,
+      ScrollbarOrientation orientation,
+      ScrollbarAnimationControllerClient* client,
+      base::CancelableClosure* delayed_scrollbar_fade,
+      base::TimeDelta thinning_duration);
+
+  float AnimationProgressAtTime(base::TimeTicks now);
+  void RunAnimationFrame(float progress);
+  const base::TimeDelta& Duration();
+
+  // Describes whether the current animation should INCREASE (thicken)
+  // a bar or DECREASE it (thin).
+  enum AnimationChange { NONE, INCREASE, DECREASE };
+  float ThumbThicknessScaleAt(float progress);
+
+  float AdjustScale(float new_value,
+                    float current_value,
+                    AnimationChange animation_change,
+                    float min_value,
+                    float max_value);
+  void ApplyThumbThicknessScale(float thumb_thickness_scale);
+
+  ScrollbarAnimationControllerClient* client_;
+  base::CancelableClosure* delayed_scrollbar_fade_;
+
+  base::TimeTicks last_awaken_time_;
+  bool is_animating_;
+
+  int scroll_layer_id_;
+
+  ScrollbarOrientation orientation_;
+  bool hidden_;
+  bool captured_;
+  bool mouse_is_over_scrollbar_;
+  bool mouse_is_near_scrollbar_;
+  // Are we narrowing or thickening the bars.
+  AnimationChange thickness_change_;
+  // How close should the mouse be to the scrollbar before we thicken it.
+  float mouse_move_distance_to_trigger_animation_;
+
+  base::TimeDelta thinning_duration_;
+
+  DISALLOW_COPY_AND_ASSIGN(SingleScrollbarAnimationControllerThinning);
+};
+
+}  // namespace cc
+
+#endif  // CC_INPUT_SINGLE_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_