Implement correct clipping for image filters.

src/effects/SkBlurImageFilter.cpp

Index: src/effects/SkBlurImageFilter.cpp
diff --git a/src/effects/SkBlurImageFilter.cpp b/src/effects/SkBlurImageFilter.cpp
index ccc7ec386631cff597223232d3d2ab34cb2be3cb..67b0511480eaff63c99272f722c2bb2951f71e3a 100644
--- a/src/effects/SkBlurImageFilter.cpp
+++ b/src/effects/SkBlurImageFilter.cpp
@@ -236,6 +236,21 @@ void SkBlurImageFilter::computeFastBounds(const SkRect& src, SkRect* dst) const
     dst->outset(SkScalarMul(fSigma.width(), SkIntToScalar(3)),
                 SkScalarMul(fSigma.height(), SkIntToScalar(3)));
 }
+
+bool SkBlurImageFilter::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
+                                       SkIRect* dst) const {
+    SkIRect bounds = src;
+    if (getInput(0) && !getInput(0)->filterBounds(src, ctm, &bounds)) {
+        return false;
+    }
+    SkVector sigma, localSigma = SkVector::Make(fSigma.width(), fSigma.height());
+    ctm.mapVectors(&sigma, &localSigma, 1);
+    bounds.outset(SkScalarCeilToInt(SkScalarMul(sigma.x(), SkIntToScalar(3))),
+                  SkScalarCeilToInt(SkScalarMul(sigma.y(), SkIntToScalar(3))));
+    *dst = bounds;
+    return true;
+}
+
 bool SkBlurImageFilter::filterImageGPU(Proxy* proxy, const SkBitmap& src, const SkMatrix& ctm,
                                        SkBitmap* result, SkIPoint* offset) {
 #if SK_SUPPORT_GPU