Implement difference clip rects with window rectangles

src/gpu/GrNonAtomicRef.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrNonAtomicRef_DEFINED
 #define GrNonAtomicRef_DEFINED
 
@@ skipping 10 matching lines @@
 
 #ifdef SK_DEBUG
     ~GrNonAtomicRef() {
         // fRefCnt can be one when a subclass is created statically
         SkASSERT((0 == fRefCnt || 1 == fRefCnt));
         // Set to invalid values.
         fRefCnt = -10;
     }
 #endif
 
+    bool unique() const { return 1 == fRefCnt; }
+
     void ref() const {
         // Once the ref cnt reaches zero it should never be ref'ed again.
         SkASSERT(fRefCnt > 0);
         ++fRefCnt;
     }
 
     void unref() const {
         SkASSERT(fRefCnt > 0);
         --fRefCnt;
         if (0 == fRefCnt) {
             GrTDeleteNonAtomicRef(static_cast<const TSubclass*>(this));
             return;
         }
     }
 
 private:
     mutable int32_t fRefCnt;
 
     typedef SkNoncopyable INHERITED;
 };
 
 template<typename T> inline void GrTDeleteNonAtomicRef(const T* ref) {
     delete ref;
 }
 
 #endif