cc: Make BackToBackBeginFrameSource a SyntheticBeginFrameSource.

content/renderer/gpu/compositor_external_begin_frame_source.cc

Index: content/renderer/gpu/compositor_external_begin_frame_source.cc
diff --git a/content/renderer/gpu/compositor_external_begin_frame_source.cc b/content/renderer/gpu/compositor_external_begin_frame_source.cc
index a8b76cf2e87366d30dde269a15e5a982054592ba..e2d13608ac781ece2ba7576d23a3ef8cade0cfb6 100644
--- a/content/renderer/gpu/compositor_external_begin_frame_source.cc
+++ b/content/renderer/gpu/compositor_external_begin_frame_source.cc
@@ -32,19 +32,19 @@ CompositorExternalBeginFrameSource::~CompositorExternalBeginFrameSource() {
   }
 }
 
-void CompositorExternalBeginFrameSource::OnNeedsBeginFramesChanged(
-    bool needs_begin_frames) {
-  DCHECK(CalledOnValidThread());
-  if (!needs_begin_frames)
-    missed_begin_frame_args_ = cc::BeginFrameArgs();
-  Send(new ViewHostMsg_SetNeedsBeginFrames(routing_id_, needs_begin_frames));
-}
-
 void CompositorExternalBeginFrameSource::AddObserver(
     cc::BeginFrameObserver* obs) {
   DCHECK(CalledOnValidThread());
+  DCHECK(obs);
+  DCHECK(observers_.find(obs) == observers_.end());
+
   SetClientReady();
-  BeginFrameSourceBase::AddObserver(obs);
+  bool observers_was_empty = observers_.empty();
+  observers_.insert(obs);
+  obs->OnBeginFrameSourcePausedChanged(paused_);
+  if (observers_was_empty)
+    Send(new ViewHostMsg_SetNeedsBeginFrames(routing_id_, true));
+
   // Send a MISSED begin frame if necessary.
   if (missed_begin_frame_args_.IsValid()) {
     cc::BeginFrameArgs last_args = obs->LastUsedBeginFrameArgs();
@@ -55,6 +55,18 @@ void CompositorExternalBeginFrameSource::AddObserver(
   }
 }
 
+void CompositorExternalBeginFrameSource::RemoveObserver(
+    cc::BeginFrameObserver* obs) {
+  DCHECK(obs);
+  DCHECK(observers_.find(obs) != observers_.end());
+
+  observers_.erase(obs);
+  if (observers_.empty()) {
+    missed_begin_frame_args_ = cc::BeginFrameArgs();
+    Send(new ViewHostMsg_SetNeedsBeginFrames(routing_id_, false));
+  }
+}
+
 void CompositorExternalBeginFrameSource::SetClientReady() {
   DCHECK(CalledOnValidThread());
   if (begin_frame_source_proxy_)
@@ -74,17 +86,30 @@ void CompositorExternalBeginFrameSource::OnMessageReceived(
   DCHECK(CalledOnValidThread());
   DCHECK(begin_frame_source_proxy_.get());
   IPC_BEGIN_MESSAGE_MAP(CompositorExternalBeginFrameSource, message)
-    IPC_MESSAGE_HANDLER(ViewMsg_SetBeginFramePaused, SetBeginFrameSourcePaused)
+    IPC_MESSAGE_HANDLER(ViewMsg_SetBeginFramePaused,
+                        OnSetBeginFrameSourcePaused)
     IPC_MESSAGE_HANDLER(ViewMsg_BeginFrame, OnBeginFrame)
   IPC_END_MESSAGE_MAP()
 }
 
+void CompositorExternalBeginFrameSource::OnSetBeginFrameSourcePaused(
+    bool paused) {
+  if (paused_ == paused)
+    return;
+  paused_ = paused;
+  std::unordered_set<cc::BeginFrameObserver*> observers(observers_);
+  for (auto* obs : observers)
+    obs->OnBeginFrameSourcePausedChanged(paused_);
+}
+
 void CompositorExternalBeginFrameSource::OnBeginFrame(
   const cc::BeginFrameArgs& args) {
   DCHECK(CalledOnValidThread());
   missed_begin_frame_args_ = args;
   missed_begin_frame_args_.type = cc::BeginFrameArgs::MISSED;
-  CallOnBeginFrame(args);
+  std::unordered_set<cc::BeginFrameObserver*> observers(observers_);
+  for (auto* obs : observers)
+    obs->OnBeginFrame(args);
 }
 
 bool CompositorExternalBeginFrameSource::Send(IPC::Message* message) {