Bug 1151890 - Explicitly set a null MessageLoop for the APZ controller thread on OS X. r=mstange

widget/cocoa/nsChildView.h

@@ -560,6 +560,7 @@ protected:
   }
 
   void ConfigureAPZCTreeManager() override;
+  void ConfigureAPZControllerThread() override;
 
   void DoRemoteComposition(const nsIntRect& aRenderRect);
 

widget/cocoa/nsChildView.mm

@@ -60,6 +60,7 @@
 #include "ScopedGLHelpers.h"
 #include "HeapCopyOfStackArray.h"
 #include "mozilla/layers/APZCTreeManager.h"
+#include "mozilla/layers/APZThreadUtils.h"
 #include "mozilla/layers/GLManager.h"
 #include "mozilla/layers/CompositorOGL.h"
 #include "mozilla/layers/CompositorParent.h"
@@ -1890,6 +1891,14 @@ nsChildView::ConfigureAPZCTreeManager()
   gNumberOfWidgetsNeedingEventThread++;
 }
 
+void
+nsChildView::ConfigureAPZControllerThread()
+{
+  // On OS X the EventThreadRunner is the controller thread, but it doesn't
+  // have a MessageLoop.
+  APZThreadUtils::SetControllerThread(nullptr);
+}
+
 nsIntRect
 nsChildView::RectContainingTitlebarControls()
 {