Fix bugs in clip parent calculations

Source/core/rendering/compositing/CompositingReasonFinder.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/rendering/compositing/CompositingReasonFinder.h"
 
 #include "core/CSSPropertyNames.h"
 #include "core/dom/Document.h"
 #include "core/frame/FrameView.h"
@@ skipping 136 matching lines @@
 
     return renderer->hasFilter();
 }
 
 CompositingReasons CompositingReasonFinder::nonStyleDeterminedDirectReasons(const RenderLayer* layer) const
 {
     CompositingReasons directReasons = CompositingReasonNone;
     RenderObject* renderer = layer->renderer();
 
     if (hasOverflowScrollTrigger()) {
+        if (layer->clipParent())
+            directReasons |= CompositingReasonOutOfFlowClipping;
+
         if (const RenderLayer* scrollingAncestor = layer->ancestorScrollingLayer()) {
-            if (scrollingAncestor->needsCompositedScrolling()) {
-                if (layer->clipParent())
-                    directReasons |= CompositingReasonOutOfFlowClipping;
-
-                if (layer->scrollParent())
-                    directReasons |= CompositingReasonOverflowScrollingParent;
-            }
+            if (scrollingAncestor->needsCompositedScrolling() && layer->scrollParent())
+                directReasons |= CompositingReasonOverflowScrollingParent;
         }
 
         if (layer->needsCompositedScrolling())
             directReasons |= CompositingReasonOverflowScrollingTouch;
     }
 
     if (requiresCompositingForPositionFixed(renderer, layer, 0))
         directReasons |= CompositingReasonPositionFixed;
 
     directReasons |= renderer->additionalCompositingReasons(m_compositingTriggers);
@@ skipping 84 matching lines @@
             if (viewportConstrainedNotCompositedReason)
                 *viewportConstrainedNotCompositedReason = RenderLayer::NotCompositedForBoundsOutOfView;
             return false;
         }
     }
 
     return true;
 }
 
 }