move skpdiff into tools

tools/skpdiff/SkImageDiffer.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmap.h"
 #include "SkImageDecoder.h"
 
@@ skipping 16 matching lines @@
     if (!SkImageDecoder::DecodeFile(baseline, &baselineBitmap)) {
         SkDebugf("Failed to load bitmap \"%s\"\n", baseline);
         return -1;
     }
     if (!SkImageDecoder::DecodeFile(test, &testBitmap)) {
         SkDebugf("Failed to load bitmap \"%s\"\n", test);
         return -1;
     }
     return this->queueDiff(&baselineBitmap, &testBitmap);
 }