Revert of make getContentKey() available in GrGpuResource public interface

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 170 matching lines @@
         return fGpuMemorySize;
     }
 
     /**
      * Gets an id that is unique for this GrGpuResource object. It is static in that it does
      * not change when the content of the GrGpuResource object changes. This will never return
      * 0.
      */
     uint32_t getUniqueID() const { return fUniqueID; }
 
-    /** Returns the current content key for the resource. It will be invalid if the resource has not
-        been cached by its contents. */
-    const GrContentKey& getContentKey() const { return fContentKey; }
-
     /**
      * Attach a custom data object to this resource. The data will remain attached
      * for the lifetime of this resource (until it is abandoned or released).
      * Takes a ref on data. Previously attached data, if any, is unrefed.
      * Returns the data argument, for convenience.
      */
     const SkData* setCustomData(const SkData* data);
 
     /**
      * Returns the custom data object that was attached to this resource by
@@ skipping 86 matching lines @@
     LifeCycle                   fLifeCycle;
     const uint32_t              fUniqueID;
 
     SkAutoTUnref<const SkData>  fData;
 
     typedef GrIORef<GrGpuResource> INHERITED;
     friend class GrIORef<GrGpuResource>; // to access notifyIsPurgeable.
 };
 
 #endif