Add reference-counting for mailbox textures.

content/common/gpu/gpu_channel.cc

Index: content/common/gpu/gpu_channel.cc
diff --git a/content/common/gpu/gpu_channel.cc b/content/common/gpu/gpu_channel.cc
index b7231b4c9610fab8e6f02f6375a6c696918d260e..e9ddd9def6b6f27891b3766421a930b59af3fc04 100644
--- a/content/common/gpu/gpu_channel.cc
+++ b/content/common/gpu/gpu_channel.cc
@@ -945,4 +945,10 @@ void GpuChannel::CacheShader(const std::string& key,
       new GpuHostMsg_CacheShader(client_id_, key, shader));
 }
 
+void GpuChannel::OnDestroySurface(int route_id, int surface_id) {
+  GpuCommandBufferStub* stub = LookupCommandBuffer(route_id);
+  if (stub)
+    stub->OnDestroySurface(surface_id);
+}
+
 }  // namespace content