Implement correct clipping for image filters.

src/effects/SkDisplacementMapEffect.cpp

Index: src/effects/SkDisplacementMapEffect.cpp
diff --git a/src/effects/SkDisplacementMapEffect.cpp b/src/effects/SkDisplacementMapEffect.cpp
index e56cba1b4b884bcee22c4fa5044bca32295b7894..555f795a519c36ff8d4414a614e174b337bf5865 100644
--- a/src/effects/SkDisplacementMapEffect.cpp
+++ b/src/effects/SkDisplacementMapEffect.cpp
@@ -255,6 +255,15 @@ void SkDisplacementMapEffect::computeFastBounds(const SkRect& src, SkRect* dst)
     }
 }
 
+bool SkDisplacementMapEffect::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
+                                   SkIRect* dst) const {
+    if (getColorInput()) {
+        return getColorInput()->filterBounds(src, ctm, dst);
+    }
+    *dst = src;
+    return true;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 #if SK_SUPPORT_GPU