[Chromecast] Don't use system libexpat.

third_party/expat/expat.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': {
     'conditions': [
       # On Linux, we implicitly already depend on expat via fontconfig;
       # let's not pull it in twice.
-      ['os_posix == 1 and OS != "mac" and OS != "ios" and OS != "android"', {
+      ['os_posix==1 and OS!="mac" and OS!="ios" and OS!="android" and chromecast!=1', {
         'use_system_expat%': 1,
       }, {
         'use_system_expat%': 0,
       }],
     ],
   },
   'target_defaults': {
     'defines': [
       '_LIB',
       'XML_STATIC',  # Compile for static linkage.
@@ skipping 38 matching lines @@
             'defines': [
               'XML_STATIC',  # Tell dependants to expect static linkage.
             ],
           },
           'conditions': [
             ['OS=="win"', {
               'defines': [
                 'COMPILED_FROM_DSP',
               ],
             }],
-            ['OS=="mac" or OS=="ios" or OS=="android" or os_bsd==1', {
+            ['OS=="mac" or OS=="ios" or OS=="android" or os_bsd==1 or chromecast==1', {
               'defines': [
                 'HAVE_EXPAT_CONFIG_H',
               ],
             }],
           ],
         },
       ],
     }],
   ],
 }