Make the Skia GN build work.

skia/skia_pdfium.gypi

 # Copyright 2013 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.
 
 
-# This gypi file contains all the Chrome-specific enhancements to Skia.
+# This gypi file contains all the PDFium-specific enhancements to Skia.
 # In component mode (shared_lib) it is folded into a single shared library with
 # the Skia files but in all other cases it is a separate library.
 {
   'dependencies': [
     'skia_library',
   ],
 
   'direct_dependent_settings': {
     'include_dirs': [
       'ext',
     ],
   },
   'variables': {
     # TODO(scottmg): http://crbug.com/177306
     'clang_warning_flags_unset': [
       # Don't warn about string->bool used in asserts.
       '-Wstring-conversion',
     ],
   },
   'sources': [
+    'config/SkUserConfig.h',
     'ext/google_logging.cc',
   ],
 }