Implement fade-out animation for Aura overlay scrollbars (CC only).

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 {
 
 ScrollbarAnimationController::ScrollbarAnimationController(
     int scroll_layer_id,
     ScrollbarAnimationControllerClient* client,
     base::TimeDelta delay_before_starting,
     base::TimeDelta resize_delay_before_starting,
     base::TimeDelta duration)
     : client_(client),
+      duration_(duration),
       delay_before_starting_(delay_before_starting),
       resize_delay_before_starting_(resize_delay_before_starting),
-      duration_(duration),
       is_animating_(false),
       scroll_layer_id_(scroll_layer_id),
       currently_scrolling_(false),
       scroll_gesture_has_scrolled_(false),
       weak_factory_(this) {}
 
 ScrollbarAnimationController::~ScrollbarAnimationController() {}
 
 bool ScrollbarAnimationController::Animate(base::TimeTicks now) {
   if (!is_animating_)
@@ skipping 16 matching lines @@
   float progress = delta.InSecondsF() / duration_.InSecondsF();
   return std::max(std::min(progress, 1.f), 0.f);
 }
 
 void ScrollbarAnimationController::DidScrollBegin() {
   currently_scrolling_ = true;
 }
 
 void ScrollbarAnimationController::DidScrollUpdate(bool on_resize) {
   StopAnimation();
-  delayed_scrollbar_fade_.Cancel();
 
   // As an optimization, we avoid spamming fade delay tasks during active fast
   // scrolls.  But if we're not within one, we need to post every scroll update.
+  // TODO(bokan): When do we get ScrollUpdates without a ScrollBegin? This may

[aelias_OOO_until_Jul13, 2016/10/20 23:40:51]

Any kind of main-thread scroll (JS, history or gesture handling).

[bokan, 2016/10/21 00:32:30]

Got it, thanks. Removed TODO and added a test.

+  // be unsupported behavior at this point.
   if (!currently_scrolling_)
     PostDelayedAnimationTask(on_resize);
   else
     scroll_gesture_has_scrolled_ = true;
 }
 
 void ScrollbarAnimationController::DidScrollEnd() {
   if (scroll_gesture_has_scrolled_) {
     PostDelayedAnimationTask(false);
     scroll_gesture_has_scrolled_ = false;
@@ skipping 13 matching lines @@
 }
 
 void ScrollbarAnimationController::StartAnimation() {
   delayed_scrollbar_fade_.Cancel();
   is_animating_ = true;
   last_awaken_time_ = base::TimeTicks();
   client_->SetNeedsAnimateForScrollbarAnimation();
 }
 
 void ScrollbarAnimationController::StopAnimation() {
+  delayed_scrollbar_fade_.Cancel();
   is_animating_ = false;
 }
 
 ScrollbarSet ScrollbarAnimationController::Scrollbars() const {
   return client_->ScrollbarsFor(scroll_layer_id_);
 }
 
 }  // namespace cc