Bug 1066242 - Use a 'ui' chromium message loop/pump for the Windows compositor thread so that it can process native windowing events. r=Bas

gfx/layers/ipc/CompositorParent.cpp

@@ -149,6 +149,12 @@ CompositorThreadHolder::CreateCompositorThread()
    * Compositor hangs seen in the wild, but is short enough to not miss getting
    * native hang stacks. */
   options.permanent_hang_timeout = 2048; // milliseconds
+#if defined(_WIN32)
+  /* With d3d9 the compositor thread creates native ui, see DeviceManagerD3D9. As
+   * such the thread is a gui thread, and must process a windows message queue or
+   * risk deadlocks. Chromium message loop TYPE_UI does exactly what we need. */
+  options.message_loop_type = MessageLoop::TYPE_UI;
+#endif
 
   if (!compositorThread->StartWithOptions(options)) {
     delete compositorThread;