remove double including of libpng decoder

gm/gmmain.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /*
  * Code for the "gm" (Golden Master) rendering comparison tool.
  *
  * If you make changes to this, re-run the self-tests at gm/tests/run.sh
  * to make sure they still pass... you may need to change the expected
  * results of the self-test.
  */
 
 #include "gm.h"
 #include "gm_error.h"
 #include "gm_expectations.h"
 #include "system_preferences.h"
 #include "SkBitmap.h"
 #include "SkColorPriv.h"
 #include "SkCommandLineFlags.h"
 #include "SkData.h"
 #include "SkDeferredCanvas.h"
 #include "SkDevice.h"
 #include "SkDrawFilter.h"
+#include "SkForceLinking.h"
 #include "SkGPipe.h"
 #include "SkGraphics.h"
 #include "SkImageDecoder.h"
 #include "SkImageEncoder.h"
 #include "SkOSFile.h"
 #include "SkPicture.h"
 #include "SkRefCnt.h"
 #include "SkStream.h"
 #include "SkTArray.h"
 #include "SkTDict.h"
 #include "SkTileGridPicture.h"
 #include "SamplePipeControllers.h"
 
+__SK_FORCE_IMAGE_DECODER_LINKING;
+
 #ifdef SK_BUILD_FOR_WIN
     // json includes xlocale which generates warning 4530 because we're compiling without
     // exceptions; see https://code.google.com/p/skia/issues/detail?id=1067
     #pragma warning(push)
     #pragma warning(disable : 4530)
 #endif
 #include "json/value.h"
 #ifdef SK_BUILD_FOR_WIN
     #pragma warning(pop)
 #endif
@@ skipping 2037 matching lines @@
     if (FLAGS_forceBWtext) {
         canvas->setDrawFilter(SkNEW(BWTextDrawFilter))->unref();
     }
 }
 
 #if !defined(SK_BUILD_FOR_IOS) && !defined(SK_BUILD_FOR_NACL)
 int main(int argc, char * const argv[]) {
     return tool_main(argc, (char**) argv);
 }
 #endif