Enable BeginFrame scheduling on aura

content/browser/renderer_host/begin_frame_observer_proxy.cc

Index: content/browser/renderer_host/begin_frame_observer_proxy.cc
diff --git a/content/browser/renderer_host/begin_frame_observer_proxy.cc b/content/browser/renderer_host/begin_frame_observer_proxy.cc
index 7a6651f53c3a9faf6d55e981e1838d333563dd5a..06baa18bd2a128390dd6436cf581077043c0f5fc 100644
--- a/content/browser/renderer_host/begin_frame_observer_proxy.cc
+++ b/content/browser/renderer_host/begin_frame_observer_proxy.cc
@@ -14,6 +14,7 @@ BeginFrameObserverProxy::BeginFrameObserverProxy(
 }
 
 BeginFrameObserverProxy::~BeginFrameObserverProxy() {
+  DCHECK(!compositor_);
 }
 
 void BeginFrameObserverProxy::SetNeedsBeginFrames(bool needs_begin_frames) {
@@ -38,6 +39,7 @@ void BeginFrameObserverProxy::SetCompositor(ui::Compositor* compositor) {
   DCHECK(compositor);
 
   compositor_ = compositor;
+  compositor_->AddObserver(this);
   if (needs_begin_frames_)
     StartObservingBeginFrames();
 }
@@ -45,6 +47,7 @@ void BeginFrameObserverProxy::SetCompositor(ui::Compositor* compositor) {
 void BeginFrameObserverProxy::ResetCompositor() {
   if (!compositor_)
     return;
+  compositor_->RemoveObserver(this);
 
   if (needs_begin_frames_)
     StopObservingBeginFrames();
@@ -57,6 +60,11 @@ void BeginFrameObserverProxy::OnSendBeginFrame(const cc::BeginFrameArgs& args) {
   last_sent_begin_frame_args_ = args;
 }
 
+void BeginFrameObserverProxy::OnCompositingShuttingDown(
+    ui::Compositor* compositor) {
+  ResetCompositor();
+}
+
 void BeginFrameObserverProxy::StartObservingBeginFrames() {
   DCHECK(compositor_);
   compositor_->AddBeginFrameObserver(this);