Fix cc scrollbar layer issues with initialization, and use element ids throughout.

cc/input/scrollbar_animation_controller.h

 // Copyright 2012 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_H_
 #define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_
 
 #include "base/cancelable_callback.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
@@ skipping 26 matching lines @@
 // SingleScrollbarAnimationControllerThinnings.
 class CC_EXPORT ScrollbarAnimationController {
  public:
   // ScrollbarAnimationController for Android. It only has show & fade out
   // animation.
   static std::unique_ptr<ScrollbarAnimationController>
   CreateScrollbarAnimationControllerAndroid(
       ElementId scroll_element_id,
       ScrollbarAnimationControllerClient* client,
       base::TimeDelta fade_delay,
-      base::TimeDelta fade_duration);
+      base::TimeDelta fade_duration,
+      float initial_opacity);
 
   // ScrollbarAnimationController for Desktop Overlay Scrollbar. It has show &
   // fade out animation and thinning animation.
   static std::unique_ptr<ScrollbarAnimationController>
   CreateScrollbarAnimationControllerAuraOverlay(
       ElementId scroll_element_id,
       ScrollbarAnimationControllerClient* client,
       base::TimeDelta fade_delay,
       base::TimeDelta fade_duration,
-      base::TimeDelta thinning_duration);
+      base::TimeDelta thinning_duration,
+      float initial_opacity);
 
   ~ScrollbarAnimationController();
 
   bool ScrollbarsHidden() const;
 
   bool Animate(base::TimeTicks now);
 
   // WillUpdateScroll expects to be called even if the scroll position won't
   // change as a result of the scroll. Only effect Aura Overlay Scrollbar.
   void WillUpdateScroll();
@@ skipping 13 matching lines @@
   // Called when Blink wants to show the scrollbars (via
   // ScrollableArea::showOverlayScrollbars).
   void DidRequestShowFromMainThread();
 
   // These methods are public for testing.
   bool MouseIsOverScrollbarThumb(ScrollbarOrientation orientation) const;
   bool MouseIsNearScrollbarThumb(ScrollbarOrientation orientation) const;
   bool MouseIsNearScrollbar(ScrollbarOrientation orientation) const;
   bool MouseIsNearAnyScrollbar() const;
 
+  ScrollbarSet Scrollbars() const;
+
   static constexpr float kMouseMoveDistanceToTriggerFadeIn = 30.0f;
 
  private:
   // Describes whether the current animation should FadeIn or FadeOut.
   enum AnimationChange { NONE, FADE_IN, FADE_OUT };
 
   ScrollbarAnimationController(ElementId scroll_element_id,
                                ScrollbarAnimationControllerClient* client,
                                base::TimeDelta fade_delay,
-                               base::TimeDelta fade_duration);
+                               base::TimeDelta fade_duration,
+                               float initial_opacity);
 
   ScrollbarAnimationController(ElementId scroll_element_id,
                                ScrollbarAnimationControllerClient* client,
                                base::TimeDelta fade_delay,
                                base::TimeDelta fade_duration,
-                               base::TimeDelta thinning_duration);
+                               base::TimeDelta thinning_duration,
+                               float initial_opacity);
 
-  ScrollbarSet Scrollbars() const;
   SingleScrollbarAnimationControllerThinning& GetScrollbarAnimationController(
       ScrollbarOrientation) const;
 
   // Returns how far through the animation we are as a progress value from
   // 0 to 1.
   float AnimationProgressAtTime(base::TimeTicks now);
   void RunAnimationFrame(float progress);
 
   void StartAnimation();
   void StopAnimation();
@@ skipping 34 matching lines @@
       vertical_controller_;
   std::unique_ptr<SingleScrollbarAnimationControllerThinning>
       horizontal_controller_;
 
   base::WeakPtrFactory<ScrollbarAnimationController> weak_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_