compositor: Add rAF-like functionality for the UI.

ui/compositor/layer_animator_collection.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 "ui/compositor/layer_animator_collection.h"
 
 #include <set>
 
 #include "base/time/time.h"
 #include "ui/compositor/layer_animator.h"
 #include "ui/gfx/frame_time.h"
 
 namespace ui {
 
 LayerAnimatorCollection::LayerAnimatorCollection(
-    LayerAnimatorCollectionDelegate* delegate)
-    : delegate_(delegate),
-      last_tick_time_(gfx::FrameTime::Now()) {
+    AnimationFrameTaskProvider* provider)
+    : provider_(provider), last_tick_time_(gfx::FrameTime::Now()) {
 }
 
 LayerAnimatorCollection::~LayerAnimatorCollection() {
 }
 
 void LayerAnimatorCollection::StartAnimator(
     scoped_refptr<LayerAnimator> animator) {
   DCHECK_EQ(0U, animators_.count(animator));
   if (!animators_.size())
     last_tick_time_ = gfx::FrameTime::Now();
   animators_.insert(animator);
-  if (delegate_)
-    delegate_->ScheduleAnimationForLayerCollection();
+  if (!raf_callback_ && provider_)
+    raf_callback_ = provider_->RequestAnimationFrameTask(this);
 }
 
 void LayerAnimatorCollection::StopAnimator(
     scoped_refptr<LayerAnimator> animator) {
   DCHECK_GT(animators_.count(animator), 0U);
   animators_.erase(animator);
+  if (animators_.empty() && raf_callback_)
+    raf_callback_.reset();
 }
 
 bool LayerAnimatorCollection::HasActiveAnimators() const {
   return !animators_.empty();
 }
 
-void LayerAnimatorCollection::Progress(base::TimeTicks now) {
+AnimationFrameTaskStatus LayerAnimatorCollection::Progress(
+    base::TimeTicks now) {
   last_tick_time_ = now;
   std::set<scoped_refptr<LayerAnimator> > list = animators_;
   for (std::set<scoped_refptr<LayerAnimator> >::iterator iter = list.begin();
        iter != list.end();
        ++iter) {
     // Make sure the animator is still valid.
     if (animators_.count(*iter) > 0)
       (*iter)->Step(now);
   }
+  return HasActiveAnimators() ? ANIMATION_FRAME_TASK_CONTINUE
+                              : ANIMATION_FRAME_TASK_END;
 }
 
 }  // namespace ui