Implement merging non-composited paint property nodes in the PACompositor.

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

 // Copyright 2015 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 "core/paint/PaintPropertyTreeBuilder.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutInline.h"
@@ skipping 288 matching lines @@
 
   if (object.paintProperties() && object.paintProperties()->transform()) {
     context.current.transform = object.paintProperties()->transform();
     context.current.shouldFlattenInheritedTransform = false;
     context.current.renderingContextID = 0;
   }
 }
 
 static CompositingReasons compositingReasonsForTransform(
     const LayoutObject& object) {
+  
   CompositingReasons compositingReasons = CompositingReasonNone;
   if (CompositingReasonFinder::requiresCompositingForTransform(object))
     compositingReasons |= CompositingReason3DTransform;
 
   if (CompositingReasonFinder::requiresCompositingForTransformAnimation(
           object.styleRef()))
     compositingReasons |= CompositingReasonActiveAnimation;
 
   if (object.styleRef().hasWillChangeCompositingHint() &&
       !object.styleRef().subtreeWillChangeContents())
     compositingReasons |= CompositingReasonWillChangeCompositingHint;
 
+  if (object.isBoxModelObject()) {
+    const LayoutBoxModelObject* box = toLayoutBoxModelObject(&object);
+    if (box->hasLayer()) {
+      // TODO(chrishtr): move this to the descendant-dependent flags recursion
+      // PaintLayer::updateDescendantDependentFlags.
+      box->layer()->update3DTransformedDescendantStatus();
+
+      if (box->layer()->has3DTransformedDescendant())
+        compositingReasons |= CompositingReason3DTransform;
+    }
+  }
+
   return compositingReasons;
 }
 
 static FloatPoint3D transformOrigin(const LayoutBox& box) {
   const ComputedStyle& style = box.styleRef();
   // Transform origin has no effect without a transform or motion path.
   if (!style.hasTransform())
     return FloatPoint3D();
   FloatSize borderBoxSize(box.size());
   return FloatPoint3D(
@@ skipping 640 matching lines @@
   updateOverflowClip(object, context);
   updatePerspective(object, context);
   updateSvgLocalToBorderBoxTransform(object, context);
   updateScrollAndScrollTranslation(object, context);
   updateOutOfFlowContext(object, context);
 
   context.forceSubtreeUpdate |= object.subtreeNeedsPaintPropertyUpdate();
 }
 
 }  // namespace blink