Implement the framework for the paint property hierarchy

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

Index: third_party/WebKit/Source/platform/graphics/paint/PaintProperties.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintProperties.h b/third_party/WebKit/Source/platform/graphics/paint/PaintProperties.h
index 69a6651de7ed9dc39f562fcb2b79e711512dbbb6..cfd9780e84b1d3b70b3bef0dd82780b78bb6ddc4 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintProperties.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintProperties.h
@@ -5,21 +5,26 @@
 #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)