ozone: Allow loading the platform implementation from a system library.

PRESUBMIT.py

 # 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.
 
 """Top-level presubmit script for Chromium.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
 
@@ skipping 151 matching lines @@
       (
        'New code should not use ScopedAllowIO. Post a task to the blocking',
        'pool or the FILE thread instead.',
       ),
       True,
       (
         r"^components[\\\/]breakpad[\\\/]app[\\\/]breakpad_mac\.mm$",
         r"^content[\\\/]shell[\\\/]browser[\\\/]shell_browser_main\.cc$",
         r"^content[\\\/]shell[\\\/]browser[\\\/]shell_message_filter\.cc$",
         r"^mojo[\\\/]system[\\\/]raw_shared_buffer_posix\.cc$",
+        r"^ui[\\\/]ozone[\\\/]ozone_platform\.cc$",
         r"^net[\\\/]disk_cache[\\\/]cache_util\.cc$",
       ),
     ),
     (
       'SkRefPtr',
       (
         'The use of SkRefPtr is prohibited. ',
         'Please use skia::RefPtr instead.'
       ),
       True,
@@ skipping 1358 matching lines @@
     builders.extend(['cros_x86'])
 
   # The AOSP bot doesn't build the chrome/ layer, so ignore any changes to it
   # unless they're .gyp(i) files as changes to those files can break the gyp
   # step on that bot.
   if (not all(re.search('^chrome', f) for f in files) or
       any(re.search('\.gypi?$', f) for f in files)):
     builders.extend(['android_aosp'])
 
   return GetDefaultTryConfigs(builders)