Implement correct clipping for image filters.

src/effects/SkBitmapSource.cpp

Index: src/effects/SkBitmapSource.cpp
diff --git a/src/effects/SkBitmapSource.cpp b/src/effects/SkBitmapSource.cpp
index 67567c5039b5dc925a0b79df351ec8e3855a2fe1..f318c91a73d890602bb63f448d8b15ec57e4530c 100644
--- a/src/effects/SkBitmapSource.cpp
+++ b/src/effects/SkBitmapSource.cpp
@@ -83,3 +83,9 @@ bool SkBitmapSource::onFilterImage(Proxy* proxy, const SkBitmap&, const SkMatrix
 void SkBitmapSource::computeFastBounds(const SkRect&, SkRect* dst) const {
     *dst = fDstRect;
 }
+
+bool SkBitmapSource::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
+                                    SkIRect* dst) const {
+    *dst = src;
+    return true;
+}