add asAShadowBlur for android to drawlooper

include/core/SkMaskFilter.h

Index: include/core/SkMaskFilter.h
diff --git a/include/core/SkMaskFilter.h b/include/core/SkMaskFilter.h
index 3113c93442764541f45df1d1d508a7884de7a827..dfa5ebac3b5a624ffbda145d392772fb977d9a59 100644
--- a/include/core/SkMaskFilter.h
+++ b/include/core/SkMaskFilter.h
@@ -10,6 +10,7 @@
 #ifndef SkMaskFilter_DEFINED
 #define SkMaskFilter_DEFINED
 
+#include "SkBlurTypes.h"
 #include "SkFlattenable.h"
 #include "SkMask.h"
 #include "SkPaint.h"
@@ -138,6 +139,13 @@ public:
      */
     virtual void computeFastBounds(const SkRect& src, SkRect* dest) const;
 
+    struct BlurRec {
+        SkScalar        fSigma;
+        SkBlurStyle     fStyle;
+        SkBlurQuality   fQuality;
+    };
+    virtual bool asABlur(BlurRec*) const;
+
     SK_TO_STRING_PUREVIRT()
     SK_DEFINE_FLATTENABLE_TYPE(SkMaskFilter)