Turns on use_mojo=1 for linux.

content/content_browsertests.isolate

 # 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.
 {
   'conditions': [
     ['OS=="android"', {
       'variables': {
         'isolate_dependency_tracked': [
           '<(PRODUCT_DIR)/content_shell/assets/content_shell.pak',
         ],
@@ skipping 15 matching lines @@
           '<(PRODUCT_DIR)/content_browsertests<(EXECUTABLE_SUFFIX)',
           '--test-launcher-bot-mode',
         ],
         'isolate_dependency_tracked': [
           '../testing/xvfb.py',
           '<(PRODUCT_DIR)/content_shell.pak',
           '<(PRODUCT_DIR)/fonts.conf',
           '<(PRODUCT_DIR)/libclearkeycdm.so',
           '<(PRODUCT_DIR)/libclearkeycdmadapter.so',
           '<(PRODUCT_DIR)/libffmpegsumo.so',
+          '<(PRODUCT_DIR)/lib/libmojo_system.so',
           '<(PRODUCT_DIR)/plugins/libtest_netscape_plugin.so',
           '<(PRODUCT_DIR)/plugins/libnpapi_test_plugin.so',
         ],
       },
     }],
     ['OS=="linux" or OS=="mac" or OS=="win"', {
       'variables': {
         'isolate_dependency_tracked': [
           '../testing/test_env.py',
           '<(PRODUCT_DIR)/content_browsertests<(EXECUTABLE_SUFFIX)',
@@ skipping 41 matching lines @@
           '<(PRODUCT_DIR)/clearkeycdmadapter.dll',
           '<(PRODUCT_DIR)/content_shell.pak',
           '<(PRODUCT_DIR)/mojo_system.dll',
           '<(PRODUCT_DIR)/plugins/np_test_netscape_plugin.dll',
           '<(PRODUCT_DIR)/plugins/npapi_test_plugin.dll',
         ],
       },
     }],
   ],
 }