Make GrResourceCache use a priority queue of purgeable resources.

include/gpu/GrGpuResource.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGpuResource_DEFINED
 #define GrGpuResource_DEFINED
 
@@ skipping 251 matching lines @@
     void setScratchKey(const GrScratchKey& scratchKey);
 
 private:
     /**
      * Frees the object in the underlying 3D API. Called by CacheAccess.
      */
     void release();
 
     virtual size_t onGpuMemorySize() const = 0;
 
-    // See comments in CacheAccess.
+    // See comments in CacheAccess and ResourcePriv.
     bool setContentKey(const GrContentKey& contentKey);
     void removeContentKey();
     void notifyIsPurgeable() const;
     void removeScratchKey();
     void makeBudgeted();
     void makeUnbudgeted();
 
 #ifdef SK_DEBUG
     friend class GrGpu; // for assert in GrGpu to access getGpu
 #endif
 
     static uint32_t CreateUniqueID();
 
-    // We're in an internal doubly linked list owned by GrResourceCache
+    // We're in an internal doubly linked list owned by GrResourceCache. TODO: Replace this with an
+    // array of unpurgeable resources in the cache.
     SK_DECLARE_INTERNAL_LLIST_INTERFACE(GrGpuResource);
 
+    // An index into a heap when this resource is purgeable. This is maintained by the cache.
+    int                         fCacheArrayIndex;
+    // This value reflects how recently this resource was accessed in the cache. This is maintained
+    // by the cache.
+    uint32_t                    fTimestamp;
 
     static const size_t kInvalidGpuMemorySize = ~static_cast<size_t>(0);
     GrScratchKey                fScratchKey;
     GrContentKey                fContentKey;
 
     // This is not ref'ed but abandon() or release() will be called before the GrGpu object
     // is destroyed. Those calls set will this to NULL.
     GrGpu*                      fGpu;
     mutable size_t              fGpuMemorySize;
 
     LifeCycle                   fLifeCycle;
     const uint32_t              fUniqueID;
 
     SkAutoTUnref<const SkData>  fData;
 
     typedef GrIORef<GrGpuResource> INHERITED;
     friend class GrIORef<GrGpuResource>; // to access notifyIsPurgeable.
 };
 
 #endif