Added method to synchronize command buffers within GpuControl.

gpu/command_buffer/client/gpu_control.h

Index: gpu/command_buffer/client/gpu_control.h
diff --git a/gpu/command_buffer/client/gpu_control.h b/gpu/command_buffer/client/gpu_control.h
index d637a1ddcb8c28254d3c64499636c2eaa8698168..1d14fe57ad21f4f72537368b6944dcb4449bc132 100644
--- a/gpu/command_buffer/client/gpu_control.h
+++ b/gpu/command_buffer/client/gpu_control.h
@@ -86,6 +86,15 @@ class GPU_EXPORT GpuControl {
   // should be considered as lost.
   virtual bool IsGpuChannelLost() = 0;
 
+  // This command forces the server to the synchronized with the client by
+  // sending a synchronous IPC. Once this function returns, it is guaranteed
+  // that the server will have received any asynchronous commands previously
+  // sent by this command buffer. Note just that it is received does not
+  // necessarily mean that it has been processed. This is only relevant for
+  // out of process servers and will be treated as a NOP for in process
+  // command buffers.
+  virtual void SynchronizeCommandBuffer() = 0;

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

Sorry for the bikeshed, but I would prefer a more descriptive name (because we
have many kind of synchronization, it's really unclear from the name what it
means).

How about: EnsureWorkVisible() ? When it returns all the previously flushed work
is visible by the service.

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

Done.

+
   // The namespace and command buffer ID forms a unique pair for all existing
   // GpuControl (on client) and matches for the corresponding command buffer
   // (on server) in a single server process. The extra command buffer data can