Add Visual Studio 2013 to the autodetect list

BUG=377
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/55493003

git-svn-id: http://gyp.googlecode.com/svn/trunk@1776 78cadc50-ecff-11dd-a971-7dbc132099af
diff --git a/pylib/gyp/MSVSVersion.py b/pylib/gyp/MSVSVersion.py
index c36b774..0ef427e 100644
--- a/pylib/gyp/MSVSVersion.py
+++ b/pylib/gyp/MSVSVersion.py
@@ -376,7 +376,7 @@
   if version == 'auto':
     version = os.environ.get('GYP_MSVS_VERSION', 'auto')
   version_map = {
-    'auto': ('10.0', '9.0', '8.0', '11.0'),
+    'auto': ('10.0', '12.0', '9.0', '8.0', '11.0'),
     '2005': ('8.0',),
     '2005e': ('8.0',),
     '2008': ('9.0',),