Fix the MessageLoop type in case more than one ozone platform is built

ui/ozone/platform/x11/ozone_platform_x11.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/ozone/platform/x11/ozone_platform_x11.h"
 
 #include <X11/Xlib.h>
 
 #include <memory>
 #include <utility>
@@ skipping 86 matching lines @@
     cursor_factory_ozone_.reset(new X11CursorFactoryOzone());
     gpu_platform_support_host_.reset(CreateStubGpuPlatformSupportHost());
   }
 
   void InitializeGPU() override {
     if (!event_source_)
       event_source_.reset(new X11EventSourceLibevent(gfx::GetXDisplay()));
     surface_factory_ozone_.reset(new X11SurfaceFactory());
   }
 
+  base::MessageLoop::Type GetMessageLoopTypeForGpu() override {
+    // When Ozone X11 backend is running use an UI loop to grab Expose events.
+    // See GLSurfaceGLX and https://crbug.com/326995.
+    return base::MessageLoop::TYPE_UI;
+  }
+
  private:
   // Objects in the browser process.
   std::unique_ptr<X11WindowManagerOzone> window_manager_;
   std::unique_ptr<OverlayManagerOzone> overlay_manager_;
   std::unique_ptr<InputController> input_controller_;
   std::unique_ptr<X11CursorFactoryOzone> cursor_factory_ozone_;
   std::unique_ptr<GpuPlatformSupportHost> gpu_platform_support_host_;
 
   // Objects in the GPU process.
   std::unique_ptr<X11SurfaceFactory> surface_factory_ozone_;
 
   // Objects in both browser and GPU process.
   std::unique_ptr<X11EventSourceLibevent> event_source_;
 
   DISALLOW_COPY_AND_ASSIGN(OzonePlatformX11);
 };
 
 }  // namespace
 
 OzonePlatform* CreateOzonePlatformX11() {
   return new OzonePlatformX11;
 }
 
 }  // namespace ui