[Chromecast] Don't use system libexpat.

third_party/expat/BUILD.gn

Index: third_party/expat/BUILD.gn
diff --git a/third_party/expat/BUILD.gn b/third_party/expat/BUILD.gn
index 78ddb0531c33e35d58350e2801aefa545738fac7..c5e2ccf1329631616f08ad0baed5ed96b07dd065 100644
--- a/third_party/expat/BUILD.gn
+++ b/third_party/expat/BUILD.gn
@@ -2,7 +2,9 @@
 # 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" ]
   }