Optimize CSS box-shadow performance by caching the SkMask of the blur effect.

include/core/SkMaskFilter.h

Index: include/core/SkMaskFilter.h
diff --git a/include/core/SkMaskFilter.h b/include/core/SkMaskFilter.h
index 72f20af21fbb5698522f96d1883316e75c8d23ca..8797c5b2483dbf7a754f5e6ef40915ae6986a1c4 100644
--- a/include/core/SkMaskFilter.h
+++ b/include/core/SkMaskFilter.h
@@ -165,7 +165,7 @@ protected:
     };
 
     struct NinePatch {
-        SkMask      fMask;      // fBounds must have [0,0] in its top-left
+        SkDiscardableMemoryMask fDiscardableMemoryMask; // fBounds must have [0,0] in its top-left
         SkIRect     fOuterRect; // width/height must be >= fMask.fBounds'
         SkIPoint    fCenter;    // identifies center row/col for stretching
     };