Turns on use_mojo=1 for linux.

chrome/tools/build/linux/FILES.cfg

 # -*- python -*-
 # ex: set syntax=python:
 
 # 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.
 
 # This is a buildbot configuration file containing a tagged list of files
 # processed by the stage/archive scripts. The known tags are:
 #
@@ skipping 46 matching lines @@
   },
   {
     'filename': 'installer',
     'buildtype': ['official'],
   },
   {
     'filename': 'libffmpegsumo.so',
     'buildtype': ['dev', 'official'],
   },
   {
+    'filename': 'lib/libmojo_system.so',
+    'buildtype': ['dev', 'official'],

[mmoss, 2014/03/20 02:24:09]

If this is in fact optional for Linux, then you should add:
'optional': ['dev', 'official'],

[sky, 2014/03/20 14:51:40]

Added along with a TODO.

+  },
+  {
     'filename': 'lib/libpeerconnection.so',
     'buildtype': ['dev', 'official'],
     'optional': ['dev', 'official'],
   },
   {
     'filename': 'locales',
     'buildtype': ['dev', 'official'],
   },
   {
     'filename': 'product_logo_48.png',
@@ skipping 142 matching lines @@
     'buildtype': ['official'],
     'archive': 'chrome-linux-nacl-irt-syms.zip',
   },
   {
     'filename': 'nacl_irt_x86_64.nexe.debug',
     'arch': ['64bit'],
     'buildtype': ['official'],
     'archive': 'chrome-linux-nacl-irt-syms.zip',
   },
 ]