ozone: Add post message loop initialization hook

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 d27709a94890b9979c9b14eb3fe4e4ddf3641de5..14a8e2d428d2b87cae5f81e269621b728de86337 100644
--- a/ui/ozone/public/ozone_platform.h
+++ b/ui/ozone/public/ozone_platform.h
@@ -50,6 +50,12 @@ class OZONE_EXPORT OzonePlatform {
   // Initializes the subsystems/resources necessary for the GPU process.
   static void InitializeForGPU();
 
+  // Initializes the subsystems/resources necessary for the GPU process, after
+  // the message loop is started. This is used mainly for initialization tasks
+  // that need to take a reference to the UI thread MessageLoopProxy.
+  // InitializeForGPU() necessarily needs to be called first.
+  static void InitializeForGpuPostMainLoop();
+
   static OzonePlatform* GetInstance();
 
   // Factory getters to override in subclasses. The returned objects will be
@@ -70,6 +76,7 @@ class OZONE_EXPORT OzonePlatform {
  private:
   virtual void InitializeUI() = 0;
   virtual void InitializeGPU() = 0;
+  virtual void InitializeGpuPostMainLoop() = 0;
 
   static void CreateInstance();