Decouple BrowserCompositorOutputSurface from BeginFrameSource.

ui/compositor/compositor_vsync_manager.cc

Index: ui/compositor/compositor_vsync_manager.cc
diff --git a/ui/compositor/compositor_vsync_manager.cc b/ui/compositor/compositor_vsync_manager.cc
index 2bc25fc0275e22fbd3fcb5a4a79d1676f06bf708..f8a5a30662a11915a1e64e161b6072a364bb6398 100644
--- a/ui/compositor/compositor_vsync_manager.cc
+++ b/ui/compositor/compositor_vsync_manager.cc
@@ -28,12 +28,12 @@ void CompositorVSyncManager::UpdateVSyncParameters(base::TimeTicks timebase,
   NotifyObservers(timebase, interval);
 }
 
-void CompositorVSyncManager::AddObserver(Observer* observer) {
+void CompositorVSyncManager::AddObserver(cc::VSyncObserver* observer) {
   observer_list_.AddObserver(observer);
   observer->OnUpdateVSyncParameters(last_timebase_, last_interval_);
 }
 
-void CompositorVSyncManager::RemoveObserver(Observer* observer) {
+void CompositorVSyncManager::RemoveObserver(cc::VSyncObserver* observer) {
   observer_list_.RemoveObserver(observer);
 }