Revert of [build] Use MSVS 2015 by default.

build/vs_toolchain.py

 #!/usr/bin/env python
 # Copyright 2015 the V8 project authors. All rights reserved.
 # Copyright 2014 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.
 
 import glob
 import json
 import os
 import pipes
 import shutil
 import subprocess
 import sys
 
 
 script_dir = os.path.dirname(os.path.realpath(__file__))
 chrome_src = os.path.abspath(os.path.join(script_dir, os.pardir))
 SRC_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 sys.path.insert(1, os.path.join(chrome_src, 'tools'))
 sys.path.insert(0, os.path.join(chrome_src, 'build', 'gyp', 'pylib'))
 json_data_file = os.path.join(script_dir, 'win_toolchain.json')
 
 
 import gyp
 
 
-# Use MSVS2015 as the default toolchain.
-CURRENT_DEFAULT_TOOLCHAIN_VERSION = '2015'
+# Use MSVS2013 as the default toolchain.
+CURRENT_DEFAULT_TOOLCHAIN_VERSION = '2013'
 
 
 def SetEnvironmentAndGetRuntimeDllDirs():
   """Sets up os.environ to use the depot_tools VS toolchain with gyp, and
   returns the location of the VS runtime DLLs so they can be copied into
   the output directory after gyp generation.
   """
   vs_runtime_dll_dirs = None
   depot_tools_win_toolchain = \
       bool(int(os.environ.get('DEPOT_TOOLS_WIN_TOOLCHAIN', '1')))
@@ skipping 331 matching lines @@
       'copy_dlls': CopyDlls,
   }
   if len(sys.argv) < 2 or sys.argv[1] not in commands:
     print >>sys.stderr, 'Expected one of: %s' % ', '.join(commands)
     return 1
   return commands[sys.argv[1]](*sys.argv[2:])
 
 
 if __name__ == '__main__':
   sys.exit(main())