Fix the build.

src/images/SkImageDecoder.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkImageDecoder.h"
 #include "SkBitmap.h"
@@ skipping 330 matching lines @@
 }
 
 namespace {
     /**
      *  This function leaks, but that is okay because it is not intended
      *  to be called. It is only here so that the linker will include the
      *  decoders.
      *  Make sure to keep it in sync with images.gyp, so only the encoders
      *  which are created on a platform are linked.
      */
+    void force_linking();
     void force_linking() {
         SkASSERT(false);
         CreateJPEGImageDecoder();
         CreateWEBPImageDecoder();
         CreateBMPImageDecoder();
         CreateICOImageDecoder();
         CreateWBMPImageDecoder();
         // Only link GIF and PNG on platforms that build them. See images.gyp
 #if !defined(SK_BUILD_FOR_MAC) && !defined(SK_BUILD_FOR_WIN) && !defined(SK_BUILD_FOR_NACL)
         CreateGIFImageDecoder();
 #endif
 #if !defined(SK_BUILD_FOR_MAC) && !defined(SK_BUILD_FOR_WIN)
         CreatePNGImageDecoder();
 #endif
     }
 }