Constify SkPicture in DrawingDisplayItem (cc side)

cc/blink/web_display_item_list_impl.h

Index: cc/blink/web_display_item_list_impl.h
diff --git a/cc/blink/web_display_item_list_impl.h b/cc/blink/web_display_item_list_impl.h
index cd35975caeb5ae531bf631108b993ab6a674aa41..cdccb1dc4ea57f262eefd85d4cff3c9693236ab4 100644
--- a/cc/blink/web_display_item_list_impl.h
+++ b/cc/blink/web_display_item_list_impl.h
@@ -14,6 +14,7 @@
 #include "third_party/WebKit/public/platform/WebFloatPoint.h"
 #include "third_party/WebKit/public/platform/WebVector.h"
 #include "third_party/skia/include/core/SkRegion.h"
+#include "ui/gfx/geometry/point_f.h"
 
 class SkImageFilter;
 class SkMatrix44;
@@ -31,8 +32,9 @@ class WebDisplayItemListImpl : public blink::WebDisplayItemList {
   scoped_refptr<cc::DisplayItemList> ToDisplayItemList();
 
   // blink::WebDisplayItemList implementation.
-  virtual void appendDrawingItem(SkPicture* picture,
-                                 const blink::WebFloatPoint& location);
+  virtual void appendDrawingItem(
+      const SkPicture*,
+      const blink::WebFloatPoint& location = gfx::PointF());
   virtual void appendClipItem(
       const blink::WebRect& clip_rect,
       const blink::WebVector<SkRRect>& rounded_clip_rects);