Incorporate ComputedStyle::hasTransform when diffing transform styles.

third_party/WebKit/Source/core/paint/PaintLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 371 matching lines @@
     box->style()->applyTransform(
         *transform, box->size(), ComputedStyle::IncludeTransformOrigin,
         ComputedStyle::IncludeMotionPath,
         ComputedStyle::IncludeIndependentTransformProperties);
     makeMatrixRenderable(*transform, compositor()->hasAcceleratedCompositing());
   }
 }
 
 void PaintLayer::updateTransform(const ComputedStyle* oldStyle,
                                  const ComputedStyle& newStyle) {
-  if (oldStyle && newStyle.transformDataEquivalent(*oldStyle))
+  // It's possible for the old and new style transform data to be equivalent
+  // while hasTransform() differs, as it checks a number of conditions aside
+  // from just the matrix, including but not limited to animation state.
+  if (oldStyle && oldStyle->hasTransform() == newStyle.hasTransform() &&
+      newStyle.transformDataEquivalent(*oldStyle)) {
     return;
+  }
 
   // hasTransform() on the layoutObject is also true when there is
   // transform-style: preserve-3d or perspective set, so check style too.
   bool hasTransform =
       layoutObject().hasTransformRelatedProperty() && newStyle.hasTransform();
   bool had3DTransform = has3DTransform();
 
   bool hadTransform = transform();
   if (hasTransform != hadTransform) {
     if (hasTransform)
@@ skipping 2846 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->enclosingLayer());
 }
 #endif