Implement proper synchronization between HW video decode IPC and CommandBuffer.

content/common/gpu/gpu_command_buffer_stub.cc

Index: content/common/gpu/gpu_command_buffer_stub.cc
diff --git a/content/common/gpu/gpu_command_buffer_stub.cc b/content/common/gpu/gpu_command_buffer_stub.cc
index a6b378e362b2380ab51913ba7a360f4a2f076ce9..bb049dd5e22407de839638cf32629a5d26ed4498 100644
--- a/content/common/gpu/gpu_command_buffer_stub.cc
+++ b/content/common/gpu/gpu_command_buffer_stub.cc
@@ -152,6 +152,8 @@ void GpuCommandBufferStub::OnInitialize(
           &GpuChannel::OnLatchCallback, base::Unretained(channel_), route_id_));
       scheduler_->SetScheduledCallback(
           NewCallback(this, &GpuCommandBufferStub::OnScheduled));
+      scheduler_->SetTokenCallback(base::Bind(
+          &GpuCommandBufferStub::OnSetToken, base::Unretained(this)));
       if (watchdog_)
         scheduler_->SetCommandProcessedCallback(
             NewCallback(this, &GpuCommandBufferStub::OnCommandProcessed));
@@ -488,6 +490,16 @@ void GpuCommandBufferStub::CommandBufferWasDestroyed() {
   HandleDeferredMessages();
 }
 
+void GpuCommandBufferStub::AddSetTokenCallback(
+    const base::Callback<void(int32)>& callback) {
+  set_token_callbacks_.push_back(callback);
+}
+
+void GpuCommandBufferStub::OnSetToken(int32 token) {
+  for (size_t i = 0; i < set_token_callbacks_.size(); ++i)
+    set_token_callbacks_[i].Run(token);
+}
+
 void GpuCommandBufferStub::ResizeCallback(gfx::Size size) {
   if (handle_ == gfx::kNullPluginWindow) {
     scheduler_->decoder()->ResizeOffscreenFrameBuffer(size);