make OpenCL optional for skpdiff

experimental/skpdiff/SkCLImageDiffer.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCLImageDiffer_DEFINED
 #define SkCLImageDiffer_DEFINED
 
@@ skipping 67 matching lines @@
 
     cl_device_id     fDevice;
     cl_context       fContext;
     cl_command_queue fCommandQueue;
 
 private:
 
     typedef SkImageDiffer INHERITED;
 };
 
-/**
- * A OpenCL differ that measures the percentage of different corresponding pixels. If the two images
- * are not the same size or have no pixels, the result will always be zero.
- */
-class SkDifferentPixelsImageDiffer : public SkCLImageDiffer {
-public:
-    virtual const char* getName() SK_OVERRIDE;
-    virtual int queueDiff(SkBitmap* baseline, SkBitmap* test) SK_OVERRIDE;
-    virtual void deleteDiff(int id) SK_OVERRIDE;
-    virtual bool isFinished(int id) SK_OVERRIDE;
-    virtual double getResult(int id) SK_OVERRIDE;
-    virtual int getPointsOfInterestCount(int id) SK_OVERRIDE;
-    virtual SkIPoint* getPointsOfInterest(int id) SK_OVERRIDE;
-
-protected:
-    virtual bool onInit() SK_OVERRIDE;
-
-private:
-    struct QueuedDiff;
-
-    SkTDArray<QueuedDiff> fQueuedDiffs;
-    cl_kernel fKernel;
-
-    typedef SkCLImageDiffer INHERITED;
-};
-
 #endif