Bug 1150376: Do not try to use D3D11 for popup windows. r=jrmuizel

widget/windows/nsWindow.cpp

@@ -6553,6 +6553,12 @@ nsWindow::ClearCompositor(nsWindow* aWindow)
   aWindow->DestroyLayerManager();
 }
 
+bool
+nsWindow::IsPopup()
+{
+  return mWindowType == eWindowType_popup;
+}
+
 bool
 nsWindow::ShouldUseOffMainThreadCompositing()
 {
@@ -6576,7 +6582,11 @@ nsWindow::GetPreferredCompositorBackends(nsTArray<LayersBackend>& aHints)
   // transparent windows so don't even try. I'm also not sure if we even
   // want to support this case. See bug 593471
   if (!(prefs.mDisableAcceleration ||
-        mTransparencyMode == eTransparencyTransparent)) {
+        mTransparencyMode == eTransparencyTransparent ||
+        IsPopup())) {
+    // See bug 1150376, D3D11 composition can cause issues on some devices
+    // on windows 7 where presentation fails randomly for windows with drop
+    // shadows.
     if (prefs.mPreferOpenGL) {
       aHints.AppendElement(LayersBackend::LAYERS_OPENGL);
     }

widget/windows/nsWindow.h

@@ -280,6 +280,7 @@ public:
 
   virtual void GetPreferredCompositorBackends(nsTArray<mozilla::layers::LayersBackend>& aHints);
 
+  bool IsPopup();
   virtual bool ShouldUseOffMainThreadCompositing();
 
 protected: