Bug 1180688 - Disable the basic compositor backend on Mac. r=mstange

widget/nsBaseWidget.cpp

@@ -1119,7 +1119,10 @@ nsBaseWidget::GetPreferredCompositorBackends(nsTArray<LayersBackend>& aHints)
     aHints.AppendElement(LayersBackend::LAYERS_OPENGL);
   }
 
+  // At the moment, BasicCompositor is broken on mac.
+#ifndef XP_MACOSX
   aHints.AppendElement(LayersBackend::LAYERS_BASIC);
+#endif
 }
 
 nsIDocument*
@@ -1175,6 +1178,13 @@ void nsBaseWidget::CreateCompositor(int aWidth, int aHeight)
     return;
   }
 
+  nsTArray<LayersBackend> backendHints;
+  GetPreferredCompositorBackends(backendHints);
+  if (backendHints.IsEmpty()) {
+    mLayerManager = nullptr;
+    return;
+  }
+
   CreateCompositorVsyncDispatcher();
   mCompositorParent = NewCompositorParent(aWidth, aHeight);
   nsRefPtr<ClientLayerManager> lm = new ClientLayerManager(this);
@@ -1192,14 +1202,10 @@ void nsBaseWidget::CreateCompositor(int aWidth, int aHeight)
 
   TextureFactoryIdentifier textureFactoryIdentifier;
   PLayerTransactionChild* shadowManager = nullptr;
-  nsTArray<LayersBackend> backendHints;
-  GetPreferredCompositorBackends(backendHints);
 
   bool success = false;
-  if (!backendHints.IsEmpty()) {
-    shadowManager = mCompositorChild->SendPLayerTransactionConstructor(
-      backendHints, 0, &textureFactoryIdentifier, &success);
-  }
+  shadowManager = mCompositorChild->SendPLayerTransactionConstructor(
+    backendHints, 0, &textureFactoryIdentifier, &success);
 
   ShadowLayerForwarder* lf = lm->AsShadowForwarder();