Fix build failures due to unused functions when building with clang on linux.

chrome/browser/ui/libgtk2ui/libgtk2ui.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 70 matching lines @@
         'x11_input_method_context_impl_gtk2.cc',
         'x11_input_method_context_impl_gtk2.h',
       ],
       'conditions': [
         ['use_gconf==0', {
           'sources!': [
             'gconf_listener.cc',
             'gconf_listener.h',
           ],
         }],
+        [ 'clang==1', {
+          # G_DEFINE_TYPE automatically generates a *get_instance_private inline function after glib 2.37.
+          # That's unused. Prevent to complain about it.
+          'cflags': [
+            '-Wno-unused-function',
+          ],
+        }],
       ],
     },
   ],
 }