Implement an SkPicture image filter source. This is required for the external-SVG reference feature…

gm/pictureimagefilter.cpp

Index: gm/pictureimagefilter.cpp
diff --git a/gm/pictureimagefilter.cpp b/gm/pictureimagefilter.cpp
index 781088ce0ed4c38181ec3fb0e8ba58f4a4af5669..5547e87b1978d82e0e24d713ebf07c1dc43cb031 100644
--- a/gm/pictureimagefilter.cpp
+++ b/gm/pictureimagefilter.cpp
@@ -72,6 +72,15 @@ protected:
         }
     }
 
+    // SkPictureImageFilter doesn't support serialization yet.
+    virtual uint32_t onGetFlags() const SK_OVERRIDE {
+        return kSkipPicture_Flag            |
+               kSkipPipe_Flag               |
+               kSkipPipeCrossProcess_Flag   |
+               kSkipTiled_Flag              |
+               kSkipScaledReplay_Flag;
+    }
+
 private:
     SkPicture fPicture;
     typedef GM INHERITED;