Do not squash invisible layers.

Source/core/rendering/compositing/RenderLayerCompositor.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 765 matching lines @@
     ASSERT(squashingState.hasMostRecentMapping);
     if (layer->scrollsWithRespectTo(&squashingState.mostRecentMapping->owningLayer()))
         return false;
 
     return true;
 }
 
 RenderLayerCompositor::CompositingStateTransitionType RenderLayerCompositor::computeCompositedLayerUpdate(RenderLayer* layer)
 {
     CompositingStateTransitionType update = NoCompositingStateChange;
-    if (needsOwnBacking(layer)) {
+    if (!layer->subtreeIsInvisible() && needsOwnBacking(layer)) {
         if (!layer->hasCompositedLayerMapping()) {
             update = AllocateOwnCompositedLayerMapping;
         }
     } else {
         if (layer->hasCompositedLayerMapping())
             update = RemoveOwnCompositedLayerMapping;
 
         if (layerSquashingEnabled()) {
-            if (requiresSquashing(layer->compositingReasons())) {
+            if (!layer->subtreeIsInvisible() && requiresSquashing(layer->compositingReasons())) {
                 // We can't compute at this time whether the squashing layer update is a no-op,
                 // since that requires walking the render layer tree.
                 update = PutInSquashingLayer;
             } else if (layer->groupedMapping() || layer->lostGroupedMapping()) {
                 update = RemoveFromSquashingLayer;
             }
         }
     }
     return update;
 }
@@ skipping 1356 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "LocalFrame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore