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..14cb2260d9bb77658946eafcfdb9826f45fe0744 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::EnsureWorkVisible() {
+  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.
   return IsFenceSyncFlushed(release);
 }