Fix Linux build failure caused by GCC 4.3/4.2 differences.

chrome/common/gfx/favicon_size.h

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_COMMON_GFX_FAVICON_SIZE_H__
 #define CHROME_COMMON_GFX_FAVICON_SIZE_H__
 
+#include "build/build_config.h"
+
 // Size (along each axis) of the favicon.
 const int kFavIconSize = 16;
 
+#if !defined(OS_LINUX)
+// GCC 4.2 complains that this function is not used, and currently
+// it's not used by any file compiled on Linux. GCC 4.3 does not complain.
+
 // If the width or height is bigger than the favicon size, a new width/height
 // is calculated and returned in width/height that maintains the aspect
 // ratio of the supplied values.
 static void calc_favicon_target_size(int* width, int* height) {
   if (*width > kFavIconSize || *height > kFavIconSize) {
     // Too big, resize it maintaining the aspect ratio.
     float aspect_ratio = static_cast<float>(*width) /
                          static_cast<float>(*height);
     *height = kFavIconSize;
     *width = static_cast<int>(aspect_ratio * *height);
     if (*width > kFavIconSize) {
       *width = kFavIconSize;
       *height = static_cast<int>(*width / aspect_ratio);
     }
   }
 }
 
+#endif  // !defined(OS_LINUX)
+
 #endif // CHROME_COMMON_GFX_FAVICON_SIZE_H__