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

include/core/SkMask.h

Index: include/core/SkMask.h
diff --git a/include/core/SkMask.h b/include/core/SkMask.h
index 5cfef970c5024fd91bd2b2767c4fd93f33d9cf8d..77e0c817d1f7e3a16aa779141596f033397db6d4 100644
--- a/include/core/SkMask.h
+++ b/include/core/SkMask.h
@@ -10,6 +10,7 @@
 #ifndef SkMask_DEFINED
 #define SkMask_DEFINED
 
+#include "SkDiscardableMemory.h"
 #include "SkRect.h"
 
 /** \class SkMask
@@ -30,6 +31,8 @@ struct SkMask {
         kCountMaskFormats = kLCD32_Format + 1
     };
 
+    SkDiscardableMemory* fDiscardableMemory;
+    bool fUseDiscardableMemory;
     uint8_t*    fImage;
     SkIRect     fBounds;
     uint32_t    fRowBytes;