Add optimization for CHROMIUM_subscribe_uniform extension.

content/common/gpu/gpu_channel_manager.h

Index: content/common/gpu/gpu_channel_manager.h
diff --git a/content/common/gpu/gpu_channel_manager.h b/content/common/gpu/gpu_channel_manager.h
index e8c9b5f5ee4ed2757cf6360d9a61062eb509fb59..7c14cee72f93cc4c534738cdb89d0438633edfd2 100644
--- a/content/common/gpu/gpu_channel_manager.h
+++ b/content/common/gpu/gpu_channel_manager.h
@@ -19,6 +19,7 @@
 #include "content/common/content_param_traits.h"
 #include "content/common/gpu/devtools_gpu_instrumentation.h"
 #include "content/common/gpu/gpu_memory_manager.h"
+#include "gpu/command_buffer/service/valuebuffer_manager.h"
 #include "ipc/ipc_listener.h"
 #include "ipc/ipc_sender.h"
 #include "ui/gfx/gpu_memory_buffer.h"
@@ -62,7 +63,8 @@ class MessageRouter;
 // managing the lifetimes of GPU channels and forwarding IPC requests from the
 // browser process to them based on the corresponding renderer ID.
 class CONTENT_EXPORT GpuChannelManager : public IPC::Listener,
-                          public IPC::Sender {
+                          public IPC::Sender,
+                          public gpu::gles2::SubscriptionRefSet::Observer {
  public:
   GpuChannelManager(MessageRouter* router,
                     GpuWatchdog* watchdog,
@@ -80,6 +82,10 @@ class CONTENT_EXPORT GpuChannelManager : public IPC::Listener,
   // Sender overrides.
   bool Send(IPC::Message* msg) override;
 
+  // SubscriptionRefSet::Observer overrides
+  void OnAddSubscription(unsigned int target) override;
+  void OnRemoveSubscription(unsigned int target) override;
+
   bool HandleMessagesScheduled();
   uint64 MessagesProcessed();
 
@@ -164,6 +170,7 @@ class CONTENT_EXPORT GpuChannelManager : public IPC::Listener,
   scoped_ptr<GpuMemoryBufferFactory> gpu_memory_buffer_factory_;
   IPC::SyncChannel* channel_;
   scoped_refptr<IPC::MessageFilter> filter_;
+  scoped_refptr<gpu::gles2::SubscriptionRefSet> subscription_ref_set_;
 
   // Member variables should appear before the WeakPtrFactory, to ensure
   // that any WeakPtrs to Controller are invalidated before its members