Default to VS2013 on Windows

build/gyp_chromium

 #!/usr/bin/env 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 script is wrapper for Chromium that adds some support for how GYP
 # is invoked by Chromium beyond what can be done in the gclient hooks.
 
 import glob
@@ skipping 453 matching lines @@
     os.environ['GYP_GENERATORS'] = 'ninja'
   if sys.platform.startswith('win') and not os.environ.get('GYP_GENERATORS'):
     os.environ['GYP_GENERATORS'] = 'ninja'
   elif sys.platform == 'darwin' and not os.environ.get('GYP_GENERATORS') and \
       not 'OS=ios' in os.environ.get('GYP_DEFINES', []):
     os.environ['GYP_GENERATORS'] = 'ninja'
 
   # If on Windows, request that depot_tools install/update the automatic
   # toolchain, and then use it (unless opted-out).
   vs2013_runtime_dll_dirs = None
-  # TODO(scottmg): Temporarily default to off, see http://crbug.com/345993.
   depot_tools_win_toolchain = \
-      bool(int(os.environ.get('DEPOT_TOOLS_WIN_TOOLCHAIN', '0')))
+      bool(int(os.environ.get('DEPOT_TOOLS_WIN_TOOLCHAIN', '1')))
   if sys.platform in ('win32', 'cygwin') and depot_tools_win_toolchain:
     import find_depot_tools
     depot_tools_path = find_depot_tools.add_depot_tools_to_path()
     temp_handle, data_file = tempfile.mkstemp(suffix='.json')
     os.close(temp_handle)
     get_toolchain_args = [
         sys.executable,
         os.path.join(depot_tools_path,
                     'win_toolchain',
                     'get_toolchain_if_necessary.py'),
@@ skipping 69 matching lines @@
   print 'Running build/landmines.py...'
   subprocess.check_call(
       [sys.executable, os.path.join(script_dir, 'landmines.py')])
 
   if vs2013_runtime_dll_dirs:
     x64_runtime, x86_runtime = vs2013_runtime_dll_dirs
     CopyVsRuntimeDlls(os.path.join(chrome_src, GetOutputDirectory()),
                       (x86_runtime, x64_runtime))
 
   sys.exit(gyp_rc)