For GOOGLE3, add deref method to SkRefCnt.

include/core/SkRefCnt.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkRefCnt_DEFINED
 #define SkRefCnt_DEFINED
 
@@ skipping 116 matching lines @@
     mutable std::atomic<int32_t> fRefCnt;
 
     typedef SkNoncopyable INHERITED;
 };
 
 #ifdef SK_REF_CNT_MIXIN_INCLUDE
 // It is the responsibility of the following include to define the type SkRefCnt.
 // 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
 
 ///////////////////////////////////////////////////////////////////////////////
 
 /** Helper macro to safely assign one SkRefCnt[TS]* to another, checking for
     null in on each side of the assignment, and ensuring that ref() is called
     before unref(), in case the two pointers point to the same object.
  */
 #define SkRefCnt_SafeAssign(dst, src)   \
     do {                                \
@@ skipping 305 matching lines @@
  *
  *  This function may be helpful while we convert callers from ptr-based to sk_sp-based parameters.
  */
 template <typename T> sk_sp<T> sk_ref_sp(T* obj) {
     return sk_sp<T>(SkSafeRef(obj));
 }
 
 #endif
 
 #endif