Serialize DisplayListRecordingSource to protos.

cc/test/skia_common.h

Index: cc/test/skia_common.h
diff --git a/cc/test/skia_common.h b/cc/test/skia_common.h
index 2351e278d0cba53db09712b4cb0ebdfc40799e36..ba5d969c79da9b48335423cb32434e349d2629e0 100644
--- a/cc/test/skia_common.h
+++ b/cc/test/skia_common.h
@@ -23,6 +23,10 @@ void DrawDisplayList(unsigned char* buffer,
                      const gfx::Rect& layer_rect,
                      scoped_refptr<DisplayItemList> list);
 
+bool AreDisplayListDrawingResultsSame(const gfx::Rect& layer_rect,
+                                      scoped_refptr<DisplayItemList> list_a,
+                                      scoped_refptr<DisplayItemList> list_b);
+
 skia::RefPtr<SkImage> CreateDiscardableImage(const gfx::Size& size);
 
 }  // namespace cc