Replace uses of GR_DEBUG by SK_DEBUG.

src/gpu/GrMemoryPool.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrMemoryPool_DEFINED
 #define GrMemoryPool_DEFINED
 
@@ skipping 54 matching lines @@
     enum {
         // We assume this alignment is good enough for everybody.
         kAlignment    = 8,
         kHeaderSize   = GR_CT_ALIGN_UP(sizeof(BlockHeader), kAlignment),
         kPerAllocPad  = GR_CT_ALIGN_UP(sizeof(BlockHeader*), kAlignment),
     };
     size_t                            fPreallocSize;
     size_t                            fMinAllocSize;
     BlockHeader*                      fHead;
     BlockHeader*                      fTail;
-#if GR_DEBUG
+#ifdef SK_DEBUG
     int                               fAllocationCnt;
 #endif
 };
 
 #endif