cc: Implement unified BeginFrame on aura

ui/base/compositor/compositor_begin_frame_observer.h

+// 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.

[mithro-old, 2014/12/16 10:50:58]

Is this being added because BeginFrameObserver in
cc/scheduler/begin_frame_source.h can't be used in ui/base?

Can cc/ depend on ui/base - if so we should probably just move the file from
cc/scheduler into ui/base/compositor

[simonhong, 2014/12/16 15:13:30]

I thought cc::BeginFrameObserver and ui:CompositorBeginFrameObserver has
different source.
Former is for BeginFrameSource and latter is for Compositor.
Both are living different layer and target.
Do we need to use same interface just because both have a similar interface?

[danakj, 2014/12/16 15:44:11]

Ui depends on cc so can't go the other way. It should stay in cc/ if its used by
cc and ui. If cc only needs a base class (interface) then it should move

[brianderson, 2014/12/17 01:44:55]

If we want to unify the Observer classes, we'll need to keep the single observer
in cc then.

Could we:
1) Get rid of the ChildrenNeedBeginFrames paths that Simon landed in a previous
patch.
2) Have the ui::Compositor own the external BeginFrameSource.
3) Only give cc::Scheduler a raw pointer to the external BeginFrameSource,
instead of having the scheduler own it. (Enne mentioned they want to do this for
Android anyway.)
4) Make RWHVA inherit and complete BeginFrameObserverMixIn.
5) Allow the RWHVA to add itself as an observer to the external BeginFrame
source that the ui::Compositor owns.

+
+#ifndef UI_BASE_COMPOSITOR_COMPOSITOR_BEGIN_FRAME_OBSERVER_H_
+#define UI_BASE_COMPOSITOR_COMPOSITOR_BEGIN_FRAME_OBSERVER_H_
+
+namespace cc {
+struct BeginFrameArgs;
+}
+
+namespace ui {
+
+class CompositorBeginFrameObserver {
+ public:
+  virtual ~CompositorBeginFrameObserver() {}
+
+  virtual void OnSendBeginFrame(const cc::BeginFrameArgs& args) = 0;
+};
+
+}  // namespace ui
+
+ #endif  // UI_BASE_COMPOSITOR_COMPOSITOR_BEGIN_FRAME_OBSERVER_H_