Add fixed raster scale use counter histograms.

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

 /*
  * Copyright (C) 2009, 2010, 2011 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 539 matching lines @@
             layerConfigChanged = true;
     }
 
     // Changes to either the internal hierarchy or the mask layer have an impact
     // on painting phases, so we need to update when either are updated.
     if (layerConfigChanged || maskLayerChanged)
         updatePaintingPhases();
 
     updateElementIdAndCompositorMutableProperties();
 
+    m_graphicsLayer->setHasWillChangeTransformHint(m_owningLayer.layoutObject()->styleRef().hasWillChangeTransformHint());

[chrishtr, 2016/05/05 20:33:07]

Can you do a quick test of a translateZ layer that adds and removes will-change,
and verify that it executes this line of code?
There are some dirty bits on the compositing code that I want to make sure this
works correctly with.

[vmpstr, 2016/05/06 19:53:48]

Yep, every will change update (with nothing else changing) hits this. 

+
     return layerConfigChanged;
 }
 
 static IntRect clipBox(LayoutBox* layoutObject)
 {
     LayoutRect result = LayoutRect(LayoutRect::infiniteIntRect());
     if (layoutObject->hasOverflowClip() || layoutObject->style()->containsPaint())
         result = layoutObject->overflowClipRect(LayoutPoint());
 
     if (layoutObject->hasClip())
@@ skipping 2010 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink