antialias matrix-image-filter to get smooth diagonals

include/core/SkImageFilter.h

Index: include/core/SkImageFilter.h
diff --git a/include/core/SkImageFilter.h b/include/core/SkImageFilter.h
index dab46ae716b69ffb76f9adcf726342289ecda4cb..bc2fae89f54723268c7a2a49ae4bd1498664626e 100644
--- a/include/core/SkImageFilter.h
+++ b/include/core/SkImageFilter.h
@@ -81,6 +81,9 @@ public:
     public:
         virtual ~Proxy() {};
 
+        /**
+         *  The returned device will be zero-initialized (transparent black)
+         */
         virtual SkBaseDevice* createDevice(int width, int height) = 0;
         // returns true if the proxy can handle this filter natively
         virtual bool canHandleImageFilter(const SkImageFilter*) = 0;
@@ -344,6 +347,12 @@ protected:
 private:
     bool usesSrcInput() const { return fUsesSrcInput; }
 
+    // Hack to optimize how we saveLayer, remove when no longer needed by SkCanvas
+    bool mayDrawWithMatrix() const { return this->onMayDrawWithMatrix(); }
+    // Return true if the subclass may draw the src transformed (e.g. w/ matrix)
+    virtual bool onMayDrawWithMatrix() const { return false; }
+    friend class SkCanvas;
+
     typedef SkFlattenable INHERITED;
     int fInputCount;
     SkImageFilter** fInputs;