compositor: Add rAF-like functionality for the UI.

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 603bf487ed24351e78771d66954301522a63d3cb..ab3d9dfaff14001703362d34cda42fd117fd5188 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -88,7 +88,7 @@ Compositor::Compositor(gfx::AcceleratedWidget widget,
       draw_on_compositing_end_(false),
       swap_state_(SWAP_NONE),
       layer_animator_collection_(this),
-      schedule_draw_factory_(this) {
+      weak_ptr_factory_(this) {
   root_web_layer_ = cc::Layer::Create();
 
   CommandLine* command_line = CommandLine::ForCurrentProcess();
@@ -183,7 +183,7 @@ void Compositor::ScheduleDraw() {
     defer_draw_scheduling_ = true;
     task_runner_->PostTask(
         FROM_HERE,
-        base::Bind(&Compositor::Draw, schedule_draw_factory_.GetWeakPtr()));
+        base::Bind(&Compositor::Draw, weak_ptr_factory_.GetWeakPtr()));
   }
 }
 
@@ -290,8 +290,23 @@ bool Compositor::HasObserver(CompositorObserver* observer) {
 }
 
 void Compositor::Animate(base::TimeTicks frame_begin_time) {
-  layer_animator_collection_.Progress(frame_begin_time);
-  if (layer_animator_collection_.HasActiveAnimators())
+  bool should_animate = false;
+  std::set<AnimationFrameTask*> tasks = rafs_;
+  for (std::set<AnimationFrameTask*>::iterator i = tasks.begin();
+       i != tasks.end();
+       ++i) {
+    AnimationFrameTask* task = *i;
+    if (!rafs_.count(task))
+      continue;
+    if (task->Progress(frame_begin_time) == ANIMATION_FRAME_TASK_CONTINUE) {
+      CHECK(rafs_.count(task));

[piman, 2014/07/31 01:17:03]

nit: DCHECK

+      should_animate = true;
+    } else {
+      DCHECK(!rafs_.count(task));
+    }
+  }

[piman, 2014/07/31 01:17:03]

maybe it's naive, but why wouldn't the standard Observer pattern work here?
Replace RequestAnimationFrameTask and RemoveAnimationFrameTask by an
Add/RemoveAnimationObserver (which would add to an ObserverList, and possibly
call SetNeedsAnimate), do a FOR_ALL_OBSERVERS here, and SetNeedsAnimate iff
there is any observer left.

+
+  if (should_animate)
     host_->SetNeedsAnimate();
 }
 
@@ -360,10 +375,6 @@ void Compositor::DidAbortSwapBuffers() {
                     OnCompositingAborted(this));
 }
 
-void Compositor::ScheduleAnimationForLayerCollection() {
-  host_->SetNeedsAnimate();
-}
-
 const cc::LayerTreeDebugState& Compositor::GetLayerTreeDebugState() const {
   return host_->debug_state();
 }
@@ -417,4 +428,21 @@ void Compositor::NotifyEnd() {
                     OnCompositingEnded(this));
 }
 
+scoped_ptr<ScopedAnimationFrameTask> Compositor::RequestAnimationFrameTask(
+    AnimationFrameTask* task) {
+  CHECK(!rafs_.count(task));
+  rafs_.insert(task);
+  host_->SetNeedsAnimate();
+  return make_scoped_ptr(new ScopedAnimationFrameTask(
+      task,
+      base::Bind(&Compositor::RemoveAnimationFrameTask,
+                 weak_ptr_factory_.GetWeakPtr(),
+                 task)));
+}
+
+void Compositor::RemoveAnimationFrameTask(AnimationFrameTask* task) {
+  CHECK(rafs_.count(task));
+  rafs_.erase(task);
+}
+
 }  // namespace ui