AU: Send board (e.g. x86-generic) to update server in query.

BUG=None
TEST=Attached Unittests

Review URL: http://codereview.chromium.org/2827032
diff --git a/update_check_action.cc b/update_check_action.cc
index 98ff3dc..fa8d697 100644
--- a/update_check_action.cc
+++ b/update_check_action.cc
@@ -74,7 +74,8 @@
       "    <o:app appid=\"" + XmlEncode(params.app_id) + "\" version=\"" +
       XmlEncode(params.app_version) + "\" "
       "lang=\"" + XmlEncode(params.app_lang) + "\" track=\"" +
-      XmlEncode(params.app_track) + "\">\n"
+      XmlEncode(params.app_track) + "\" board=\"" +
+      XmlEncode(params.os_board) + "\">\n"
       "        <o:ping active=\"0\"></o:ping>\n"
       "        <o:updatecheck></o:updatecheck>\n"
       "    </o:app>\n"