[Chromecast] Don't use system libexpat.

third_party/expat/BUILD.gn

 # Copyright (c) 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.
 
-if (is_linux) {
+import("//build/config/chromecast_build.gni")
+
+if (is_linux && !is_chromecast) {

[brettw, 2016/01/11 23:25:33]

Can this have a comment about why the checked-in expat should be used by
Chromecast? Just something like "Chromecast doesn't ship expat as a system
library" would be sufficient.

   config("expat_config") {
     libs = [ "expat" ]
   }
 
   group("expat") {
     public_configs = [ ":expat_config" ]
   }
 } else {
   config("expat_config") {
     include_dirs = [ "files/lib" ]
@@ skipping 11 matching lines @@
     public_configs = [ ":expat_config" ]
 
     defines = [ "_LIB" ]
     if (is_win) {
       defines += [ "COMPILED_FROM_DSP" ]
     } else {
       defines += [ "HAVE_EXPAT_CONFIG_H" ]
     }
   }
 }