Implement the framework for the paint property hierarchy

third_party/WebKit/Source/platform/graphics/paint/PaintProperties.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 PaintProperties_h
 #define PaintProperties_h
 
+#include "platform/graphics/paint/TransformPaintProperty.h"
+
 #include <iosfwd>
 
 namespace blink {
 
-// The set of paint properties applying to a |PaintChunk|.
-// In particular, this does not mean properties like background-color, but
-// rather the hierarchy of transforms, clips, effects, etc. that apply to a
-// contiguous chunk of drawings.
+// The set of paint properties applying to a |PaintChunk|. These properties are
+// not simple color changes but instead represent the hierachy 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|.
 struct PaintProperties {
-    // TODO(jbroman): Add actual properties.
+    // TODO(pdr): Add clip, scroll, and effect properties.
+    RefPtr<TransformPaintProperty> transform;
 };
 
-inline bool operator==(const PaintProperties&, const PaintProperties&)
+inline bool operator==(const PaintProperties& a, const PaintProperties& b)
 {
-    return true;
+    return a.transform.get() == b.transform.get();
 }
 
 inline bool operator!=(const PaintProperties& a, const PaintProperties& b)
 {
     return !(a == b);
 }
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/PaintPrinters.h.
 void PrintTo(const PaintProperties&, std::ostream*);
 
 } // namespace blink
 
 #endif // PaintProperties_h