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

include/effects/SkDisplacementMapEffect.h

Index: include/effects/SkDisplacementMapEffect.h
diff --git a/include/effects/SkDisplacementMapEffect.h b/include/effects/SkDisplacementMapEffect.h
index d789ca24f21e3e5cbb92d31733fa3755b9b15e38..d82a40ab9fe2eeb39e150035a5c7a77924997bf6 100644
--- a/include/effects/SkDisplacementMapEffect.h
+++ b/include/effects/SkDisplacementMapEffect.h
@@ -37,6 +37,8 @@ public:
                                const SkMatrix& ctm,
                                SkBitmap* dst,
                                SkIPoint* offset) SK_OVERRIDE;
+    virtual void computeFastBounds(const SkRect& src, SkRect* dst) const SK_OVERRIDE;
+
 #if SK_SUPPORT_GPU
     virtual bool canFilterImageGPU() const SK_OVERRIDE { return true; }
     virtual bool filterImageGPU(Proxy* proxy, const SkBitmap& src, const SkMatrix& ctm,
@@ -54,6 +56,8 @@ private:
     typedef SkImageFilter INHERITED;
     SkImageFilter* getDisplacementInput() { return getInput(0); }
     SkImageFilter* getColorInput() { return getInput(1); }
+    const SkImageFilter* getDisplacementInput() const { return getInput(0); }
+    const SkImageFilter* getColorInput() const { return getInput(1); }
 };
 
 #endif