Add a 'unique' method to SkRefCnt, document the usage, and add support.

src/gpu/GrContext.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrContext.h"
@@ skipping 470 matching lines @@
     if (NULL == texture) {
         return;
     }
 
     // This texture should already have a cache entry since it was once
     // attached
     GrAssert(NULL != texture->getCacheEntry());
 
     // Conceptually, the cache entry is going to assume responsibility
     // for the creation ref.
-    GrAssert(1 == texture->getRefCnt());
+    GrAssert(texture->unique());
 
     // Since this texture came from an AutoScratchTexture it should
     // still be in the exclusive pile
     fTextureCache->makeNonExclusive(texture->getCacheEntry());
 
     if (fGpu->caps()->reuseScratchTextures()) {
         this->purgeCache();
     } else {
         // When we aren't reusing textures we know this scratch texture
         // will never be reused and would be just wasting time in the cache
@@ skipping 1201 matching lines @@
         return NULL;
     }
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 #if GR_CACHE_STATS
 void GrContext::printCacheStats() const {
     fTextureCache->printStats();
 }
 #endif