Config changes to support target_os="fuchsia"

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 depot_tools.
 """
 
@@ skipping 327 matching lines @@
 
 
 _VALID_OS_MACROS = (
     # Please keep sorted.
     'OS_AIX',
     'OS_ANDROID',
     'OS_BSD',
     'OS_CAT',       # For testing.
     'OS_CHROMEOS',
     'OS_FREEBSD',
+    'OS_FUCHSIA',
     'OS_IOS',
     'OS_LINUX',
     'OS_MACOSX',
     'OS_NACL',
     'OS_NACL_NONSFI',
     'OS_NACL_SFI',
     'OS_NETBSD',
     'OS_OPENBSD',
     'OS_POSIX',
     'OS_QNX',
@@ skipping 2108 matching lines @@
       output_api,
       json_url='http://chromium-status.appspot.com/current?format=json'))
 
   results.extend(
       input_api.canned_checks.CheckPatchFormatted(input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasBugField(
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasDescription(
       input_api, output_api))
   return results