Add optimization for CHROMIUM_subscribe_uniform extension.

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 3f373bbc46f41b570cf1d4a4a15ee27f3d2ce45a..01f6ea1f85f0e62df44877dcdee77d094733e53d 100644
--- a/content/common/gpu/gpu_messages.h
+++ b/content/common/gpu/gpu_messages.h
@@ -412,6 +412,18 @@ IPC_MESSAGE_CONTROL1(GpuHostMsg_GpuMemoryUmaStats,
 // Response to GpuMsg_RelinquishResources.
 IPC_MESSAGE_CONTROL0(GpuHostMsg_ResourcesRelinquished)
 
+// Tells the browser that a context has subscribed to a new target and
+// the browser should start sending the corresponding information
+IPC_MESSAGE_CONTROL2(GpuHostMsg_AddSubscription,
+                     int32 /* client_id */,
+                     unsigned int /* target */);
+
+// Tells the browser that no contexts are subscribed to the target anymore
+// so the browser should stop sending the corresponding information
+IPC_MESSAGE_CONTROL2(GpuHostMsg_RemoveSubscription,
+                     int32 /* client_id */,
+                     unsigned int /* target */);
+
 //------------------------------------------------------------------------------
 // GPU Channel Messages
 // These are messages from a renderer process to the GPU process.