[Pepper GL] Use shared state to fix a memory leak in MapSub GL extension.

content/common/gpu/client/command_buffer_proxy_impl.h

Index: content/common/gpu/client/command_buffer_proxy_impl.h
diff --git a/content/common/gpu/client/command_buffer_proxy_impl.h b/content/common/gpu/client/command_buffer_proxy_impl.h
index ce564653415721d1b44f0a4cb6c005e1e4b674f5..01efa8f4cb62c11aaad85386dbde9fb9ada6f40b 100644
--- a/content/common/gpu/client/command_buffer_proxy_impl.h
+++ b/content/common/gpu/client/command_buffer_proxy_impl.h
@@ -141,6 +141,10 @@ class CommandBufferProxyImpl
 
   GpuChannelHost* channel() const { return channel_; }
 
+  base::SharedMemoryHandle GetSharedStateHandle() const {
+    return shared_state_shm_->handle();
+  }
+
  private:
   typedef std::map<int32, scoped_refptr<gpu::Buffer> > TransferBufferMap;
   typedef base::hash_map<uint32, base::Closure> SignalTaskMap;