allow imagefilter to manage CTM decomposition

include/core/SkImageFilter.h

Index: include/core/SkImageFilter.h
diff --git a/include/core/SkImageFilter.h b/include/core/SkImageFilter.h
index 9758fde9645cffb2254f2994925daab55507baaf..e2ec756b6c6a25a3a7e7a5592841901db9f9893e 100644
--- a/include/core/SkImageFilter.h
+++ b/include/core/SkImageFilter.h
@@ -216,6 +216,13 @@ public:
 #endif
 
     /**
+     *  ImageFilters can natively handle scaling and translate components in the CTM. Only some of
+     *  them can handle affine (or more complex) matrices. This call returns true iff the filter
+     *  and all of its (non-null) inputs can handle these more complex matrices.
+     */
+    bool canHandleAffine() const { return this->onCanHandleAffine(); }

[Stephen White, 2016/04/25 14:09:34]

<bikeshed> Could we add a noun to that? canHandleAffineMatrix() or
canHandleAffineTransforms()? </bikeshed>

+
+    /**
      * Return an imagefilter which transforms its input by the given matrix.
      */
     static sk_sp<SkImageFilter> MakeMatrixFilter(const SkMatrix& matrix,
@@ -342,6 +349,8 @@ protected:
         return false;
     }
 
+    virtual bool onCanHandleAffine() const;
+
     /** Given a "srcBounds" rect, computes destination bounds for this filter.
      *  "dstBounds" are computed by transforming the crop rect by the context's
      *  CTM, applying it to the initial bounds, and intersecting the result with