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

ui/ozone/public/ozone_platform.h

Index: ui/ozone/public/ozone_platform.h
diff --git a/ui/ozone/public/ozone_platform.h b/ui/ozone/public/ozone_platform.h
index 236924f01591b3a53d0c52d6959e7854c9f8483f..f1995c12b189ab5b32075af86d1558e0a762a666 100644
--- a/ui/ozone/public/ozone_platform.h
+++ b/ui/ozone/public/ozone_platform.h
@@ -8,6 +8,7 @@
 #include <memory>
 
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "ui/ozone/ozone_export.h"
 
 namespace display {
@@ -71,6 +72,12 @@ class OZONE_EXPORT OzonePlatform {
     bool single_process = false;
   };
 
+  // Ensures the OzonePlatform instance without doing any initialization.
+  // No-op in case the instance is already created.
+  // This is useful in order call virtual methods that depend on the ozone
+  // platform selected at runtime, e.g. ::GetMessageLoopTypeForGpu.
+  static OzonePlatform* EnsureInstance();
+
   // Initializes the subsystems/resources necessary for the UI process (e.g.
   // events, etc.)
   // TODO(rjkroege): Remove deprecated entry point (http://crbug.com/620934)
@@ -108,6 +115,10 @@ class OZONE_EXPORT OzonePlatform {
   virtual std::unique_ptr<display::NativeDisplayDelegate>
   CreateNativeDisplayDelegate() = 0;
 
+  // Returns the message loop type required for OzonePlatform instance that
+  // will be initialized for the GPU process.
+  virtual base::MessageLoop::Type GetMessageLoopTypeForGpu();
+
   // Ozone platform implementations may also choose to expose mojo interfaces to
   // internal functionality. Embedders wishing to take advantage of ozone mojo
   // implementations must invoke AddInterfaces with a valid
@@ -124,8 +135,6 @@ class OZONE_EXPORT OzonePlatform {
   virtual void InitializeUI(const InitParams& args);
   virtual void InitializeGPU(const InitParams& args);
 
-  static void CreateInstance();
-
   static OzonePlatform* instance_;
 
   DISALLOW_COPY_AND_ASSIGN(OzonePlatform);