Preliminary paint property walk implementation for SPv2

third_party/WebKit/Source/core/layout/LayoutObject.h

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index 6ee0b9bdce6c9cb1861d67f1e2495f7034223b09..f15dd1c32142da1fb87f513862d01f5aca285e17 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -43,6 +43,7 @@
 #include "core/layout/api/SelectionState.h"
 #include "core/layout/compositing/CompositingState.h"
 #include "core/layout/compositing/CompositingTriggers.h"
+#include "core/paint/ObjectPaintProperties.h"
 #include "core/style/ComputedStyle.h"
 #include "core/style/StyleInheritedData.h"
 #include "platform/geometry/FloatQuad.h"
@@ -179,7 +180,7 @@ const int showTreeCharacterOffset = 39;
 // preferredLogicalWidthsDirty.
 //
 // See the individual getters below for more details about what each width is.
-class CORE_EXPORT LayoutObject : public ImageResourceClient {
+class CORE_EXPORT LayoutObject : public ImageResourceClient, public ObjectPaintProperties::Owner {

[chrishtr, 2015/10/14 17:30:28]

We went to great lengths to avoid inheriting from DisplayItemClient, to avoid
making layout objects bigger and have more virtual function calls. Does that
reasoning apply in this case or not?

[trchen, 2015/10/14 22:51:13]

This guy has no virtual functions, it is more like a mix-in class than an
interface.
I checked with C++ spec again, an empty class takes 1 byte when used as a leaf
class, but may take 0 byte when inherited. (LayoutObject size check should catch
this if not 0.)

     friend class LayoutObjectChildList;
     WTF_MAKE_NONCOPYABLE(LayoutObject);
 public: