Back out bug 703484 on this CLOSED TREE.

gfx/layers/ipc/CompositorParent.cpp

@@ -465,6 +465,7 @@ CompositorParent::AllocPLayers(const LayersBackend &backendType)
     }
     return new ShadowLayersParent(slm, this);
   } else if (backendType == LayerManager::LAYERS_BASIC) {
+    // This require Cairo to be thread-safe
     nsRefPtr<LayerManager> layerManager = new BasicShadowLayerManager(mWidget);
     mWidget = NULL;
     mLayerManager = layerManager;

widget/windows/nsWindow.cpp

@@ -3241,20 +3241,8 @@ nsWindow::GetLayerManager(PLayersChild* aShadowManager,
     }
 
     // Fall back to software if we couldn't use any hardware backends.
-    if (!mLayerManager) {
-      // Try to use an async compositor first, if possible
-      bool useCompositor =
-        Preferences::GetBool("layers.offmainthreadcomposition.enabled", false);
-      if (useCompositor) {
-        // e10s uses the parameter to pass in the shadow manager from the TabChild
-        // so we don't expect to see it there since this doesn't support e10s.
-        NS_ASSERTION(aShadowManager == nsnull, "Async Compositor not supported with e10s");
-        CreateCompositor();
-      }
-
-      if (!mLayerManager)
-        mLayerManager = CreateBasicLayerManager();
-    }
+    if (!mLayerManager)
+      mLayerManager = CreateBasicLayerManager();
   }
 
   NS_ASSERTION(mLayerManager, "Couldn't provide a valid layer manager.");

widget/xpwidgets/nsBaseWidget.cpp

@@ -900,12 +900,8 @@ void nsBaseWidget::CreateCompositor()
     AsyncChannel *parentChannel = mCompositorParent->GetIPCChannel();
     AsyncChannel::Side childSide = mozilla::ipc::AsyncChannel::Child;
     mCompositorChild->Open(parentChannel, childMessageLoop, childSide);
-    PLayersChild* shadowManager;
-    if (mUseAcceleratedRendering) {
-      shadowManager = mCompositorChild->SendPLayersConstructor(LayerManager::LAYERS_OPENGL);
-    } else {
-      shadowManager = mCompositorChild->SendPLayersConstructor(LayerManager::LAYERS_BASIC);
-    }
+    PLayersChild* shadowManager =
+      mCompositorChild->SendPLayersConstructor(LayerManager::LAYERS_OPENGL);
 
     if (shadowManager) {
       ShadowLayerForwarder* lf = lm->AsShadowForwarder();
@@ -915,11 +911,7 @@ void nsBaseWidget::CreateCompositor()
         return;
       }
       lf->SetShadowManager(shadowManager);
-
-      if (mUseAcceleratedRendering)
-        lf->SetParentBackendType(LayerManager::LAYERS_OPENGL);
-      else
-        lf->SetParentBackendType(LayerManager::LAYERS_BASIC);
+      lf->SetParentBackendType(LayerManager::LAYERS_OPENGL);
 
       mLayerManager = lm;
     } else {
@@ -939,18 +931,18 @@ LayerManager* nsBaseWidget::GetLayerManager(PLayersChild* aShadowManager,
 
     mUseAcceleratedRendering = GetShouldAccelerate();
 
-    // Try to use an async compositor first, if possible
-    bool useCompositor =
-      Preferences::GetBool("layers.offmainthreadcomposition.enabled", false);
-    if (useCompositor) {
-      // e10s uses the parameter to pass in the shadow manager from the TabChild
-      // so we don't expect to see it there since this doesn't support e10s.
-      NS_ASSERTION(aShadowManager == nsnull, "Async Compositor not supported with e10s");
-      CreateCompositor();
-    }
-
     if (mUseAcceleratedRendering) {
 
+      // Try to use an async compositor first, if possible
+      bool useCompositor =
+        Preferences::GetBool("layers.offmainthreadcomposition.enabled", false);
+      if (useCompositor) {
+        // e10s uses the parameter to pass in the shadow manager from the TabChild
+        // so we don't expect to see it there since this doesn't support e10s.
+        NS_ASSERTION(aShadowManager == nsnull, "Async Compositor not supported with e10s");
+        CreateCompositor();
+      }
+
       if (!mLayerManager) {
         nsRefPtr<LayerManagerOGL> layerManager = new LayerManagerOGL(this);
         /**