Make GrCacheable implement its own ref counting.

include/gpu/GrContext.h

Index: include/gpu/GrContext.h
diff --git a/include/gpu/GrContext.h b/include/gpu/GrContext.h
index bdea2f94ce4c5e545a0e8d84228e4d950dd22c73..92fa881f7b3d9437d56aa038bb542d25e3373fdb 100644
--- a/include/gpu/GrContext.h
+++ b/include/gpu/GrContext.h
@@ -1119,7 +1119,7 @@ public:
         // The cache also has a ref which we are lending to the caller of detach(). When the caller
         // lets go of the ref and the ref count goes to 0 internal_dispose will see this flag is
         // set and re-ref the texture, thereby restoring the cache's ref.
-        SkASSERT(texture->getRefCnt() > 1);
+        SkASSERT(!texture->unique());
         texture->impl()->setFlag((GrTextureFlags) GrTextureImpl::kReturnToCache_FlagBit);
         texture->unref();
         SkASSERT(NULL != texture->getCacheEntry());