Remove GenMailboxCHROMIUM command

gpu/command_buffer/service/gles2_cmd_decoder_passthrough_handlers.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder_passthrough_handlers.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_handlers.cc b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_handlers.cc
index a251ea1e591b6b3291313988bf080af5786975a5..791fb21a3b3c1bb98605489a5626b6762cb467a2 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_handlers.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_handlers.cc
@@ -1511,15 +1511,6 @@ error::Error GLES2DecoderPassthroughImpl::HandleVertexAttribDivisorANGLE(
   return error::kNoError;
 }
 
-error::Error GLES2DecoderPassthroughImpl::HandleGenMailboxCHROMIUM(
-    uint32_t immediate_data_size,
-    const void* cmd_data) {
-  const gles2::cmds::GenMailboxCHROMIUM& c =
-      *static_cast<const gles2::cmds::GenMailboxCHROMIUM*>(cmd_data);
-  (void)c;
-  return error::kUnknownCommand;
-}
-
 error::Error
 GLES2DecoderPassthroughImpl::HandleBindUniformLocationCHROMIUMBucket(
     uint32_t immediate_data_size,