Don't repaint squashed, fixed position layers during scrolling

Source/core/frame/FrameView.cpp

Index: Source/core/frame/FrameView.cpp
diff --git a/Source/core/frame/FrameView.cpp b/Source/core/frame/FrameView.cpp
index c9850063e57f36439d360583b143720ad2ac1d52..e2b9d862e0298ef8b70ba9cdec69dd557b7497b5 100644
--- a/Source/core/frame/FrameView.cpp
+++ b/Source/core/frame/FrameView.cpp
@@ -1269,17 +1269,12 @@ bool FrameView::scrollContentsFastPath(const IntSize& scrollDelta)
     ViewportConstrainedObjectSet::const_iterator end = m_viewportConstrainedObjects->end();
     for (ViewportConstrainedObjectSet::const_iterator it = m_viewportConstrainedObjects->begin(); it != end; ++it) {
         RenderObject* renderer = *it;
-        // m_viewportConstrainedObjects should not contain non-viewport constrained objects.
         ASSERT(renderer->style()->hasViewportConstrainedPosition());
-
-        // Fixed items should always have layers.
         ASSERT(renderer->hasLayer());
         RenderLayer* layer = toRenderBoxModelObject(renderer)->layer();
 
-        // Layers that paint into their ancestor or into a grouped backing will still need
-        // to apply a paint invalidation. If the layer paints into its own backing, then
-        // it does not need paint invalidation just to scroll.
-        if (layer->compositingState() == PaintsIntoOwnBacking)
+        CompositingState state = layer->compositingState();
+        if (state == PaintsIntoOwnBacking || state == PaintsIntoGroupedBacking)
             continue;
 
         if (layer->hasAncestorWithFilterOutsets()) {