Now always use Atlas for layer cache

src/gpu/GrLayerCache.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 GrLayerCache_DEFINED
 #define GrLayerCache_DEFINED
 
-#define USE_ATLAS 0
-
 #include "GrAtlas.h"
 #include "GrPictureUtils.h"
 #include "GrRect.h"
 #include "SkChecksum.h"
 #include "SkTDynamicHash.h"
 #include "SkMessageBus.h"
 
 class SkPicture;
 
 // The layer cache listens for these messages to purge picture-related resources.
@@ skipping 198 matching lines @@
     // Try to find a purgeable plot and clear it out. Return true if a plot
     // was purged; false otherwise.
     bool purgePlot();
 
     // for testing
     friend class TestingAccess;
     int numLayers() const { return fLayerHash.count(); }
 };
 
 #endif