Fix iOS build of test_image_decoder

tools/test_image_decoder.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 "SkForceLinking.h"
 #include "SkGraphics.h"
 #include "SkImageDecoder.h"
 
 __SK_FORCE_IMAGE_DECODER_LINKING;
 
 /**
    Simple program to test Skia's ability to decode images without
    errors or debug messages. */
-int main(int argc, char ** argv) {
+int tool_main(int argc, char** argv);
+int tool_main(int argc, char** argv) {
     if (argc < 2) {
         SkDebugf("Usage:\n %s imagefile\n\n", argv[0]);
         return 3;
     }
     SkBitmap bitmap;
     if (!(SkImageDecoder::DecodeFile(argv[1], &bitmap))) {
         return 2;
     }
     if (bitmap.empty()) {
         return 1;
     }
     return 0;
 }
 
+#if !defined SK_BUILD_FOR_IOS
+int main(int argc, char * const argv[]) {
+    return tool_main(argc, (char**) argv);
+}
+#endif