Unified BeginFrame scheduling

ui/base/compositor/begin_frame_manager.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/base/compositor/begin_frame_manager.h"
+
+#include "cc/output/begin_frame_args.h"
+
+namespace ui {
+
+BeginFrameManager::BeginFrameManager(Delegate* delegate) : delegate_(delegate) {
+}
+
+BeginFrameManager::~BeginFrameManager() {
+}
+
+void BeginFrameManager::SendBeginFrame(
+    const cc::BeginFrameArgs& args) {
+  DCHECK(CalledOnValidThread());
+  FOR_EACH_OBSERVER(Observer,
+                    observer_list_,
+                    OnSendBeginFrame(args));
+}
+
+void BeginFrameManager::RequestBeginFrame() const {

[brianderson, 2014/08/21 00:14:00]

I think this method can be removed.

Instead, delegate_->SetChildrenNeedBeginFrames(true/false) can be called from
AddObserver when the number of observers goes from 0 to 1, and from
RemoveObserver when the number of observers goes from 1 to 0.

[simonhong, 2014/08/26 08:24:48]

Yes! This also can make code more simpler :)
Removed.

+  DCHECK(CalledOnValidThread());
+  DCHECK(delegate_);
+  delegate_->RequestBeginFrame();
+}
+
+void BeginFrameManager::AddObserver(Observer* observer) {

[brianderson, 2014/08/21 00:14:00]

You may want to make this:
void BeginFrameManager::AddObserver(Observer* observer, BeginFrameArgs
last_begin_frame_args_sent_to_observer)

And remember a last_begin_frame_args_sent in BeginFrameManager::SendBeginFrame.

Then, if last_begin_frame_args_sent_to_observer != last_begin_frame_args_sent
and last_begin_frame_args_sent.deadline hasn't passed, send
last_begin_frame_args_sent to the new observer immediately.

[simonhong, 2014/08/26 08:24:48]

Does we need more heuristics for this like "use last args if deadline is greater
than now + interval/3"?

+  DCHECK(CalledOnValidThread());
+  observer_list_.AddObserver(observer);
+}
+
+void BeginFrameManager::RemoveObserver(Observer* observer) {
+  DCHECK(CalledOnValidThread());
+  observer_list_.RemoveObserver(observer);
+}
+
+}  // namespace ui