Implement correct clipping for image filters.

include/core/SkCanvas.h

Index: include/core/SkCanvas.h
diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index c98ad996f0786caccf75d3f74dca3dbc68edda10..d9052c5ef84111484e713124c4653fb1b619148a 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -1027,8 +1027,11 @@ protected:
 
     // Clip rectangle bounds. Called internally by saveLayer.
     // returns false if the entire rectangle is entirely clipped out
+    // If non-NULL, The imageFilter parameter will be used to expand the clip
+    // and offscreen bounds for any margin required by the filter DAG.
     bool clipRectBounds(const SkRect* bounds, SaveFlags flags,
-                        SkIRect* intersection);
+                        SkIRect* intersection,
+                        const SkImageFilter* imageFilter = NULL);
 
     // Called by child classes that override clipPath and clipRRect to only
     // track fast conservative clip bounds, rather than exact clips.