For GOOGLE3, add deref method to SkRefCnt.

include/core/SkRefCnt.h

Index: include/core/SkRefCnt.h
diff --git a/include/core/SkRefCnt.h b/include/core/SkRefCnt.h
index abcda7e990bf1f89e15f33f73b3bec858271943a..46e69759cb38e994fea269dc654aebf315b05d1b 100644
--- a/include/core/SkRefCnt.h
+++ b/include/core/SkRefCnt.h
@@ -134,7 +134,13 @@ private:
 // This SkRefCnt should normally derive from SkRefCntBase.
 #include SK_REF_CNT_MIXIN_INCLUDE
 #else
-class SK_API SkRefCnt : public SkRefCntBase { };
+class SK_API SkRefCnt : public SkRefCntBase {
+    // "#include SK_REF_CNT_MIXIN_INCLUDE" doesn't work with this build system.
+    #if defined(GOOGLE3)
+    public:
+        void deref() const { this->unref(); }
+    #endif
+};
 #endif
 
 ///////////////////////////////////////////////////////////////////////////////