cc: Introduce BeginFrame sequence numbers and acknowledgements.

cc/surfaces/display.cc

Index: cc/surfaces/display.cc
diff --git a/cc/surfaces/display.cc b/cc/surfaces/display.cc
index a0ffb2ce35fce3f46f4c5674d1de15016926f006..7a6d473cfe44e4afd5e0b8a2d63d5e97742f4da6 100644
--- a/cc/surfaces/display.cc
+++ b/cc/surfaces/display.cc
@@ -42,15 +42,18 @@ Display::Display(SharedBitmapManager* bitmap_manager,
       gpu_memory_buffer_manager_(gpu_memory_buffer_manager),
       settings_(settings),
       frame_sink_id_(frame_sink_id),
-      begin_frame_source_(std::move(begin_frame_source)),
+      begin_frame_source_(
+          new DisplayBeginFrameSource(std::move(begin_frame_source))),
       output_surface_(std::move(output_surface)),
       scheduler_(std::move(scheduler)),
       texture_mailbox_deleter_(std::move(texture_mailbox_deleter)) {
   DCHECK(output_surface_);
-  DCHECK_EQ(!scheduler_, !begin_frame_source_);
+  DCHECK_EQ(!scheduler_, !begin_frame_source_->GetTargetSource());
   DCHECK(frame_sink_id_.is_valid());
-  if (scheduler_)
+  if (scheduler_) {
     scheduler_->SetClient(this);
+    scheduler_->SetBeginFrameSource(begin_frame_source_.get());
+  }
 }
 
 Display::~Display() {
@@ -58,8 +61,7 @@ Display::~Display() {
   if (client_) {
     if (auto* context = output_surface_->context_provider())
       context->SetLostContextCallback(base::Closure());
-    if (begin_frame_source_)
-      surface_manager_->UnregisterBeginFrameSource(begin_frame_source_.get());
+    surface_manager_->UnregisterBeginFrameSource(begin_frame_source_.get());
     surface_manager_->RemoveObserver(this);
   }
   if (aggregator_) {
@@ -82,10 +84,8 @@ void Display::Initialize(DisplayClient* client,
 
   // This must be done in Initialize() so that the caller can delay this until
   // they are ready to receive a BeginFrameSource.
-  if (begin_frame_source_) {
-    surface_manager_->RegisterBeginFrameSource(begin_frame_source_.get(),
-                                               frame_sink_id_);
-  }
+  surface_manager_->RegisterBeginFrameSource(begin_frame_source_.get(),
+                                             frame_sink_id_);
 
   output_surface_->BindToClient(this);
   InitializeRenderer();
@@ -403,4 +403,9 @@ void Display::ForceImmediateDrawAndSwapIfPossible() {
     scheduler_->ForceImmediateSwapIfPossible();
 }
 
+void Display::SwapBeginFrameSource(
+    std::unique_ptr<BeginFrameSource>* begin_frame_source) {
+  begin_frame_source_->SwapTargetSource(begin_frame_source);
+}
+
 }  // namespace cc