Make GrResourceCache use a priority queue of purgeable resources.

src/core/SkTDPQueue.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 SkTDPQueue_DEFINED
 #define SkTDPQueue_DEFINED
 
@@ skipping 74 matching lines @@
         allowed if an INDEX function is provided. */
     void priorityDidChange(T entry) {
         SkASSERT(NULL != INDEX);
         int index = *INDEX(entry);
         SkASSERT(index >= 0 && index < fArray.count());
         this->validate(index);
         this->percolateUpOrDown(index);
         this->validate();
     }
 
+#ifdef SK_DEBUG
+    T at(int i) const { return fArray[i]; }
+#endif
+
 private:
     static int LeftOf(int x) { SkASSERT(x >= 0); return 2 * x + 1; }
     static int ParentOf(int x) { SkASSERT(x > 0); return (x - 1) >> 1; }
 
     void percolateUpOrDown(int index) {
         SkASSERT(index >= 0);
         if (!percolateUpIfNecessary(index)) {
             this->validate(index);
             this->percolateDownIfNecessary(index);
         }
@@ skipping 77 matching lines @@
         }
 #endif
     }
 
     SkTDArray<T> fArray;
     
     typedef SkNoncopyable INHERITED;
 };
 
 #endif