Implement the algorithm to test merging and overlap in PaintArtifactCompositor.

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"
 #include "core/layout/LayoutView.h"
+#include "core/layout/compositing/CompositingReasonFinder.h"
 #include "core/layout/svg/LayoutSVGRoot.h"
 #include "core/paint/FindPropertiesNeedingUpdate.h"
 #include "core/paint/ObjectPaintProperties.h"
 #include "core/paint/PaintLayer.h"
 #include "core/paint/SVGRootPainter.h"
 #include "platform/transforms/TransformationMatrix.h"
 #include "wtf/PtrUtil.h"
 #include <memory>
 
 namespace blink {
@@ skipping 93 matching lines @@
     // specific property updates here.
     context.current.paintOffset.moveBy(frameView.location());
     context.current.renderingContextID = 0;
     context.current.shouldFlattenInheritedTransform = true;
     context.absolutePosition = context.current;
     context.containerForAbsolutePosition = nullptr;
     context.fixedPosition = context.current;
     return;
   }
 
+  m_compositingReasonFinder.reset(
+      new CompositingReasonFinder(*frameView.layoutView()));
+
 #if DCHECK_IS_ON()
   FindFrameViewPropertiesNeedingUpdateScope checkScope(&frameView, context);
 #endif
 
   if (frameView.needsPaintPropertyUpdate() || context.forceSubtreeUpdate) {
     TransformationMatrix frameTranslate;
     frameTranslate.translate(frameView.x() + context.current.paintOffset.x(),
                              frameView.y() + context.current.paintOffset.y());
     context.forceSubtreeUpdate |= updatePreTranslation(
         frameView, context.current.transform, frameTranslate, FloatPoint3D());
@@ skipping 196 matching lines @@
       // If a node with transform-style: preserve-3d does not exist in an
       // existing rendering context, it establishes a new one.
       unsigned renderingContextID = context.current.renderingContextID;
       if (style.preserves3D() && !renderingContextID)
         renderingContextID = PtrHash<const LayoutObject>::hash(&object);
 
       auto& properties = object.getMutableForPainting().ensurePaintProperties();
       context.forceSubtreeUpdate |= properties.updateTransform(
           context.current.transform, matrix,
           transformOrigin(toLayoutBox(object)),
-          context.current.shouldFlattenInheritedTransform, renderingContextID);
+          context.current.shouldFlattenInheritedTransform, renderingContextID,
+          m_compositingReasonFinder->directReasons(
+              toLayoutBoxModelObject(&object)->layer()) &
+              CompositingReason3DTransform);
     } else {
       if (auto* properties = object.getMutableForPainting().paintProperties())
         context.forceSubtreeUpdate |= properties->clearTransform();
     }
   }
 
   const auto* properties = object.paintProperties();
   if (properties && properties->transform()) {
     context.current.transform = properties->transform();
     if (object.styleRef().preserves3D()) {
@@ skipping 555 matching lines @@
 #endif
 
   updateOverflowClip(object, context);
   updatePerspective(object, context);
   updateSvgLocalToBorderBoxTransform(object, context);
   updateScrollAndScrollTranslation(object, context);
   updateOutOfFlowContext(object, context);
 }
 
 }  // namespace blink