Refactor PaintLayer location and offset calculation especially for floats

third_party/WebKit/Source/core/layout/compositing/GraphicsLayerUpdater.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Google 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
@@ skipping 36 matching lines @@
     CompositingState compositingState = layer.compositingState();
     if (compositingState != NotComposited &&
         compositingState != PaintsIntoGroupedBacking) {
       m_compositingAncestor = &layer;
       if (layer.stackingNode()->isStackingContext())
         m_compositingStackingContext = &layer;
     }
   }
 
   const PaintLayer* compositingContainer(const PaintLayer& layer) const {
-    // TODO(chrishtr) this is not very performant for floats, but they should
-    // be uncommon enough, and SPv2 will remove this code.
-    if (layer.layoutObject()->isFloating() && layer.layoutObject()->parent() &&
-        !layer.stackingNode()->isStacked() &&
-        !layer.layoutObject()->parent()->isLayoutBlockFlow()) {
+    if (layer.stackingNode()->isStacked())
+      return m_compositingStackingContext;
+
+    if (layer.layoutObject()->isFloatingWithNonContainingBlockParent())
       return layer.enclosingLayerWithCompositedLayerMapping(ExcludeSelf);
-    }
-    return layer.stackingNode()->isStacked() ? m_compositingStackingContext
-                                             : m_compositingAncestor;
+
+    return m_compositingAncestor;
   }
 
   const PaintLayer* compositingStackingContext() const {
     return m_compositingStackingContext;
   }
 
  private:
   const PaintLayer* m_compositingStackingContext;
   const PaintLayer* m_compositingAncestor;
 };
@@ skipping 54 matching lines @@
         ->assertNeedsToUpdateGraphicsLayerBitsCleared();
 
   for (PaintLayer* child = layer.firstChild(); child;
        child = child->nextSibling())
     assertNeedsToUpdateGraphicsLayerBitsCleared(*child);
 }
 
 #endif
 
 }  // namespace blink