Expose GpuMemoryBufferId through glGetImageivCHROMIUM.

ppapi/proxy/ppapi_command_buffer_proxy.cc

Index: ppapi/proxy/ppapi_command_buffer_proxy.cc
diff --git a/ppapi/proxy/ppapi_command_buffer_proxy.cc b/ppapi/proxy/ppapi_command_buffer_proxy.cc
index 77ef28217f98a9e8316a1eac4ed92494a61e62b6..b7c526486ef352b287c170bc696056a003b1d3f7 100644
--- a/ppapi/proxy/ppapi_command_buffer_proxy.cc
+++ b/ppapi/proxy/ppapi_command_buffer_proxy.cc
@@ -262,6 +262,11 @@ int32_t PpapiCommandBufferProxy::CreateGpuMemoryBufferImage(
   return -1;
 }
 
+int32_t PpapiCommandBufferProxy::GetImageGpuMemoryBufferId(unsigned image_id) {
+  NOTREACHED();
+  return -1;
+}
+
 bool PpapiCommandBufferProxy::Send(IPC::Message* msg) {
   DCHECK(last_state_.error == gpu::error::kNoError);