Add EncodeBackbufferCHROMIUM support to GLES2 command stream

content/common/gpu/gpu_command_buffer_stub.cc

Index: content/common/gpu/gpu_command_buffer_stub.cc
diff --git a/content/common/gpu/gpu_command_buffer_stub.cc b/content/common/gpu/gpu_command_buffer_stub.cc
index 26b05e5a0d9bfb11b91fd6da633e2308affbbfc9..955da1bce1b8f87f0781e69d16f18f753d2d16b8 100644
--- a/content/common/gpu/gpu_command_buffer_stub.cc
+++ b/content/common/gpu/gpu_command_buffer_stub.cc
@@ -529,6 +529,10 @@ void GpuCommandBufferStub::OnInitialize(
       base::Bind(&GpuCommandBufferStub::OnWaitSyncPoint,
                  base::Unretained(this)));
 
+  decoder_->SetEncodeBackbufferCallback(
+      base::Bind(&GpuCommandBufferStub::OnEncodeBackbuffer,
+                 base::Unretained(this)));
+
   command_buffer_->SetPutOffsetChangeCallback(
       base::Bind(&GpuCommandBufferStub::PutChanged, base::Unretained(this)));
   command_buffer_->SetGetBufferChangeCallback(
@@ -846,6 +850,9 @@ void GpuCommandBufferStub::OnSignalSyncPointAck(uint32 id) {
   Send(new GpuCommandBufferMsg_SignalSyncPointAck(route_id_, id));
 }
 
+void GpuCommandBufferStub::OnEncodeBackbuffer() {
+}
+
 void GpuCommandBufferStub::OnReceivedClientManagedMemoryStats(
     const GpuManagedMemoryStats& stats) {
   TRACE_EVENT0(