Implement a computeFastBounds() traversal for SkImageFilter. This allows for correct culling of pri…

src/effects/SkDisplacementMapEffect.cpp

Index: src/effects/SkDisplacementMapEffect.cpp
diff --git a/src/effects/SkDisplacementMapEffect.cpp b/src/effects/SkDisplacementMapEffect.cpp
index 6ad46badb9af994ec36248df5dee687a6994a86c..fc8d3dda7283f2bbf28bfacf41f81bf4ecc621ec 100644
--- a/src/effects/SkDisplacementMapEffect.cpp
+++ b/src/effects/SkDisplacementMapEffect.cpp
@@ -246,6 +246,14 @@ bool SkDisplacementMapEffect::onFilterImage(Proxy* proxy,
     return true;
 }
 
+void SkDisplacementMapEffect::computeFastBounds(const SkRect& src, SkRect* dst) const {
+    if (getColorInput()) {
+        getColorInput()->computeFastBounds(src, dst);
+    } else {
+        *dst = src;
+    }
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 #if SK_SUPPORT_GPU