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

services/ui/gpu/gpu_main.cc

Index: services/ui/gpu/gpu_main.cc
diff --git a/services/ui/gpu/gpu_main.cc b/services/ui/gpu/gpu_main.cc
index a87c7cbe39cdfe1054435e7b8eae149a32dd706b..3a528ca26a5664e60d76b7421c88b8ea8db8c41a 100644
--- a/services/ui/gpu/gpu_main.cc
+++ b/services/ui/gpu/gpu_main.cc
@@ -14,6 +14,10 @@
 #include "services/ui/common/server_gpu_memory_buffer_manager.h"
 #include "services/ui/gpu/gpu_service.h"
 
+#if defined(USE_OZONE)
+#include "ui/ozone/public/ozone_platform.h"
+#endif
+
 #if defined(OS_MACOSX)
 #include "base/message_loop/message_pump_mac.h"
 #endif
@@ -51,7 +55,12 @@ GpuMain::GpuMain(mojom::GpuMainRequest request)
 #elif defined(USE_X11)
   thread_options.message_pump_factory = base::Bind(&CreateMessagePumpX11);
 #elif defined(USE_OZONE)
-  thread_options.message_loop_type = base::MessageLoop::TYPE_UI;
+  // Create the OzonePlatform instance without doing any initialization.
+  // The MessageLoop type required depends on the Ozone platform selected at
+  // runtime.
+  ui::OzonePlatform::CreateInstance();

[sadrul, 2017/02/08 01:49:26]

We should not have this here.

[tonikitoo, 2017/02/08 02:42:34]

It was originally suggested by kyle in
https://codereview.chromium.org/2629983002/diff/60001/ui/ozone/public/ozone_p...,
and allows us to create a OzonePlatform instance without doing any
initialization, so that we can make method calls, like
::GetMessageLoopTypeForGpu

Quoting kyle, "We can't run OzonePlatform::InitializeForGPU()
before the main MessageLoop is created. Something will try and use the
MessageLoop then crash."

However, for mus today still we can call ::GetMessageLoopTypeForGpu without
calling ::CreateInstance. My understanding is that it only works because
mus-ui/mus-gpu process split has not happened yet.
I will leave up a comment with a FIXME, but the previous call to
::CreateInstance would be no-op here.

+  thread_options.message_loop_type =
+      ui::OzonePlatform::GetInstance()->GetMessageLoopTypeForGpu();
 #elif defined(OS_LINUX)
   thread_options.message_loop_type = base::MessageLoop::TYPE_DEFAULT;
 #elif defined(OS_MACOSX)