Implement the algorithm to test merging and overlap in PaintArtifactCompositor.

third_party/WebKit/Source/platform/graphics/paint/PaintChunkProperties.h

 // 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.
 
 #ifndef PaintChunkProperties_h
 #define PaintChunkProperties_h
 
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
 #include "platform/graphics/paint/ScrollPaintPropertyNode.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "wtf/Allocator.h"
 #include "wtf/Noncopyable.h"
 #include <iosfwd>
 
 namespace blink {
 
 // The set of paint properties applying to a |PaintChunk|. These properties are
 // not local-only paint style parameters such as color, but instead represent
 // the hierarchy of transforms, clips, effects, etc, that apply to a contiguous
 // chunk of display items. A single DisplayItemClient can generate multiple
 // properties of the same type and this struct represents the total state of all
 // properties for a given |PaintChunk|.
 //
 // This differs from |ObjectPaintProperties| because it only stores one property
 // for each type (e.g., either transform or perspective, but not both).
 struct PaintChunkProperties {
   DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
 
-  PaintChunkProperties() : backfaceHidden(false) {}
+  PaintChunkProperties() : backfaceHidden(false), willChangeTransform(false) {}
 
   // TODO(pdr): Refactor these to use PropertyTreeState.
   RefPtr<const TransformPaintPropertyNode> transform;
   RefPtr<const ClipPaintPropertyNode> clip;
   RefPtr<const EffectPaintPropertyNode> effect;
   RefPtr<const ScrollPaintPropertyNode> scroll;
   bool backfaceHidden;
+  bool willChangeTransform;
+
+  bool hasDirectCompositingReasons() const {
+    return backfaceHidden || willChangeTransform;
+  }
 };
 
 // Equality is based only on the pointers and is not 'deep' which would require
 // crawling the entire property tree to compute.
 inline bool operator==(const PaintChunkProperties& a,
                        const PaintChunkProperties& b) {
   return a.transform.get() == b.transform.get() &&
          a.clip.get() == b.clip.get() && a.effect.get() == b.effect.get() &&
          a.scroll.get() == b.scroll.get() &&
-         a.backfaceHidden == b.backfaceHidden;
+         a.backfaceHidden == b.backfaceHidden &&
+         a.willChangeTransform == b.willChangeTransform;
 }
 
 inline bool operator!=(const PaintChunkProperties& a,
                        const PaintChunkProperties& b) {
   return !(a == b);
 }
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/PaintPrinters.h.
 void PrintTo(const PaintChunkProperties&, std::ostream*);
 
 }  // namespace blink
 
 #endif  // PaintChunkProperties_h