Rework FlushSync to return early if commands have been processed since the last update

content/common/gpu/gpu_messages.h

Index: content/common/gpu/gpu_messages.h
diff --git a/content/common/gpu/gpu_messages.h b/content/common/gpu/gpu_messages.h
index 22c4a23bf9ed287fbe4af866f19bb2add3db3fa2..e2dbeb0da07779e4822193ceea59763a1811115e 100644
--- a/content/common/gpu/gpu_messages.h
+++ b/content/common/gpu/gpu_messages.h
@@ -341,8 +341,9 @@ IPC_MESSAGE_ROUTED0(GpuCommandBufferMsg_AsyncGetState)
 
 // Synchronize the put and get offsets of both processes. Caller passes its
 // current put offset. Current state (including get offset) is returned.
-IPC_SYNC_MESSAGE_ROUTED1_1(GpuCommandBufferMsg_Flush,
+IPC_SYNC_MESSAGE_ROUTED2_1(GpuCommandBufferMsg_Flush,
                            int32 /* put_offset */,
+                           int32 /* last_known_get */,
                            gpu::CommandBuffer::State /* state */)
 
 // Asynchronously synchronize the put and get offsets of both processes.