Use counters for opacity with transform-style:preserve-3d

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 85 matching lines @@
             ASSERT(compositingContainer == layer.enclosingLayerWithCompositedLayerMapping(ExcludeSelf));
 
             if (mapping->updateGraphicsLayerConfiguration())
                 m_needsRebuildTree = true;
 
             mapping->updateGraphicsLayerGeometry(compositingContainer, context.compositingStackingContext(), layersNeedingPaintInvalidation);
             if (PaintLayerScrollableArea* scrollableArea = layer.getScrollableArea())
                 scrollableArea->positionOverflowControls();
             updateType = mapping->updateTypeForChildren(updateType);
             mapping->clearNeedsGraphicsLayerUpdate();
+
+            const ComputedStyle& style = layer.layoutObject()->styleRef();
+            if (style.preserves3D() && style.hasOpacity() && layer.has3DTransformedDescendant())

[chrishtr, 2016/05/18 23:16:03]

Does this account for whether the child flattens itself, as opposed to being
inside the same preserves-3d
space as this element?

[chrishtr, 2016/05/18 23:22:10]

Also, I was expecting this usecounter to be in
CLM::updateGraphicsLayerConfiguration.

[trchen, 2016/05/19 00:33:28]

Done.

+                UseCounter::count(layer.layoutObject()->document(), UseCounter::OpacityWithPreserve3DQuirk);
         }
     }
 
     UpdateContext childContext(context, layer);
     for (PaintLayer* child = layer.firstChild(); child; child = child->nextSibling())
         updateRecursive(*child, updateType, childContext, layersNeedingPaintInvalidation);
 }
 
 #if ENABLE(ASSERT)
 
 void GraphicsLayerUpdater::assertNeedsToUpdateGraphicsLayerBitsCleared(PaintLayer& layer)
 {
     if (layer.hasCompositedLayerMapping())
         layer.compositedLayerMapping()->assertNeedsToUpdateGraphicsLayerBitsCleared();
 
     for (PaintLayer* child = layer.firstChild(); child; child = child->nextSibling())
         assertNeedsToUpdateGraphicsLayerBitsCleared(*child);
 }
 
 #endif
 
 } // namespace blink