Prevent overlay scrollbars expand or hover together

cc/input/scrollbar_animation_controller_client.h

Index: cc/input/scrollbar_animation_controller_client.h
diff --git a/cc/input/scrollbar_animation_controller_client.h b/cc/input/scrollbar_animation_controller_client.h
new file mode 100644
index 0000000000000000000000000000000000000000..74961db349788134e306a01d220fd40a8d02d876
--- /dev/null
+++ b/cc/input/scrollbar_animation_controller_client.h
@@ -0,0 +1,30 @@
+// Copyright 2017 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_SCROLLBAR_ANIMATION_CONTROLLER_CLIENT_H_
+#define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_CLIENT_H_
+
+#include "base/cancelable_callback.h"
+#include "base/time/time.h"
+#include "cc/base/cc_export.h"
+#include "cc/layers/scrollbar_layer_impl_base.h"
+
+namespace cc {
+
+class CC_EXPORT ScrollbarAnimationControllerClient {

[bokan, 2017/01/25 22:20:54]

Why did this have to get split out into a separate file?

+ public:
+  virtual void PostDelayedScrollbarAnimationTask(const base::Closure& task,
+                                                 base::TimeDelta delay) = 0;
+  virtual void SetNeedsRedrawForScrollbarAnimation() = 0;
+  virtual void SetNeedsAnimateForScrollbarAnimation() = 0;
+  virtual void DidChangeScrollbarVisibility() = 0;
+  virtual ScrollbarSet ScrollbarsFor(int scroll_layer_id) const = 0;
+
+ protected:
+  virtual ~ScrollbarAnimationControllerClient() {}
+};
+
+}  // namespace cc
+
+#endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_CLIENT_H_