Split toolchain update and install lookup to make generation faster

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 247 matching lines @@
   # . -f / --format has precedence over the env var, no need to check for it
   # . set the env var only if it hasn't been set yet
   # . chromium.gyp_env has been applied to os.environ at this point already
   if sys.platform.startswith(('linux', 'win', 'freebsd')) 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'
 
-  vs2013_runtime_dll_dirs = vs_toolchain.DownloadVsToolchain()
+  vs2013_runtime_dll_dirs = vs_toolchain.SetEnvironmentAndGetRuntimeDllDirs()
 
   # If CHROMIUM_GYP_SYNTAX_CHECK is set to 1, it will invoke gyp with --check
   # to enfore syntax checking.
   syntax_check = os.environ.get('CHROMIUM_GYP_SYNTAX_CHECK')
   if syntax_check and int(syntax_check):
     args.append('--check')
 
   supplemental_includes = GetSupplementalFiles()
   gyp_vars_dict = GetGypVars(supplemental_includes)
 
@@ skipping 25 matching lines @@
   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
     vs_toolchain.CopyVsRuntimeDlls(
         os.path.join(chrome_src, GetOutputDirectory()),
         (x86_runtime, x64_runtime))
 
   sys.exit(gyp_rc)