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

cc/input/scrollbar_animation_controller.cc

 // Copyright 2014 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.
 
 #include "cc/input/scrollbar_animation_controller.h"
 
 #include <algorithm>
 
 #include "base/time/time.h"
 #include "cc/trees/layer_tree_impl.h"
 
 namespace cc {
 
 std::unique_ptr<ScrollbarAnimationController>
 ScrollbarAnimationController::CreateScrollbarAnimationControllerAndroid(
     ElementId scroll_element_id,
     ScrollbarAnimationControllerClient* client,
     base::TimeDelta fade_delay,
-    base::TimeDelta fade_duration) {
+    base::TimeDelta fade_duration,
+    float initial_opacity) {
   return base::WrapUnique(new ScrollbarAnimationController(
-      scroll_element_id, client, fade_delay, fade_duration));
+      scroll_element_id, client, fade_delay, fade_duration, initial_opacity));
 }
 
 std::unique_ptr<ScrollbarAnimationController>
 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) {
   return base::WrapUnique(new ScrollbarAnimationController(
-      scroll_element_id, client, fade_delay, fade_duration, thinning_duration));
+      scroll_element_id, client, fade_delay, fade_duration, thinning_duration,
+      initial_opacity));
 }
 
 ScrollbarAnimationController::ScrollbarAnimationController(
     ElementId scroll_element_id,
     ScrollbarAnimationControllerClient* client,
     base::TimeDelta fade_delay,
-    base::TimeDelta fade_duration)
+    base::TimeDelta fade_duration,
+    float initial_opacity)
     : client_(client),
       fade_delay_(fade_delay),
       fade_duration_(fade_duration),
       need_trigger_scrollbar_fade_in_(false),
       is_animating_(false),
       animation_change_(NONE),
       scroll_element_id_(scroll_element_id),
       currently_scrolling_(false),
       show_in_fast_scroll_(false),
-      opacity_(0.0f),
+      opacity_(initial_opacity),
       show_scrollbars_on_scroll_gesture_(false),
       need_thinning_animation_(false),
-      weak_factory_(this) {
-  ApplyOpacityToScrollbars(0.0f);
-}
+      weak_factory_(this) {}
 
 ScrollbarAnimationController::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)
     : client_(client),
       fade_delay_(fade_delay),
       fade_duration_(fade_duration),
       need_trigger_scrollbar_fade_in_(false),
       is_animating_(false),
       animation_change_(NONE),
       scroll_element_id_(scroll_element_id),
       currently_scrolling_(false),
       show_in_fast_scroll_(false),
-      opacity_(0.0f),
+      opacity_(initial_opacity),
       show_scrollbars_on_scroll_gesture_(true),
       need_thinning_animation_(true),
       weak_factory_(this) {
   vertical_controller_ = SingleScrollbarAnimationControllerThinning::Create(
       scroll_element_id, ScrollbarOrientation::VERTICAL, client,
       thinning_duration);
   horizontal_controller_ = SingleScrollbarAnimationControllerThinning::Create(
       scroll_element_id, ScrollbarOrientation::HORIZONTAL, client,
       thinning_duration);
-
-  ApplyOpacityToScrollbars(0.0f);
 }
 
 ScrollbarAnimationController::~ScrollbarAnimationController() {}
 
 ScrollbarSet ScrollbarAnimationController::Scrollbars() const {
   return client_->ScrollbarsFor(scroll_element_id_);
 }
 
 SingleScrollbarAnimationControllerThinning&
 ScrollbarAnimationController::GetScrollbarAnimationController(
@@ skipping 253 matching lines @@
   if (opacity_ != opacity)
     client_->SetNeedsRedrawForScrollbarAnimation();
 
   opacity_ = opacity;
 
   if (previouslyVisible != currentlyVisible)
     client_->DidChangeScrollbarVisibility();
 }
 
 }  // namespace cc