We don't use the main_loop_ for anything, so let's create it outside, before the creation of the XWalkExtensionProcess.

XWalkExtensionProcessMain() should look like (pseudo code without namespaces):

    MessageLoop main_message_loop(base::MessageLoop::TYPE_UI);
    XWalkExtensionProcess extension_process;

    RunLoop loop;
    loop.Run();

And remove members and functions not used anymore. If in the future we need, we can pass a reference of the main loop to XWalkExtensionProcess.