Added method to synchronize command buffers within GpuControl.

ppapi/proxy/ppapi_command_buffer_proxy.cc

Index: ppapi/proxy/ppapi_command_buffer_proxy.cc
diff --git a/ppapi/proxy/ppapi_command_buffer_proxy.cc b/ppapi/proxy/ppapi_command_buffer_proxy.cc
index ecf64da26477c5428f4ae85bf52829cd99688657..e09eb252f322c10f9fae8b6e9315931d35aa39fd 100644
--- a/ppapi/proxy/ppapi_command_buffer_proxy.cc
+++ b/ppapi/proxy/ppapi_command_buffer_proxy.cc
@@ -183,6 +183,10 @@ bool PpapiCommandBufferProxy::IsGpuChannelLost() {
   return false;
 }
 
+void PpapiCommandBufferProxy::SynchronizeCommandBuffer() {
+  NOTIMPLEMENTED();
+}
+
 gpu::CommandBufferNamespace PpapiCommandBufferProxy::GetNamespaceID() const {
   return gpu::CommandBufferNamespace::GPU_IO;
 }
@@ -204,6 +208,8 @@ bool PpapiCommandBufferProxy::IsFenceSyncFlushed(uint64_t release) {
 }
 
 bool PpapiCommandBufferProxy::IsFenceSyncFlushReceived(uint64_t release) {
+  // TODO(dyen): This needs a synchronous NOP to the PpapiHost which
+  // also sends a synchronous NOP to the actual server.

[piman, 2016/01/05 00:28:38]

Can you file a bug? I don't want this to fall between the cracks, since it could
break subtly.

[David Yen, 2016/01/05 00:47:51]

Done: https://code.google.com/p/chromium/issues/detail?id=574269

   return IsFenceSyncFlushed(release);
 }