Pass "-std" flag to YCM config.

tools/vim/chromium.ycm_extra_conf.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.
 
 # Autocompletion config for YouCompleteMe in Chromium.
 #
 # USAGE:
 #
 #   1. Install YCM [https://github.com/Valloric/YouCompleteMe]
 #          (Googlers should check out [go/ycm])
@@ skipping 142 matching lines @@
   # Ninja might execute several commands to build something. We want the last
   # clang command.
   clang_line = None
   for line in reversed(stdout.split('\n')):
     if 'clang' in line:
       clang_line = line
       break
   else:
     return chrome_flags
 
-  # Parse out the -I and -D flags. These seem to be the only ones that are
-  # important for YCM's purposes.
+  # Parse flags that are important for YCM's purposes.
   for flag in clang_line.split(' '):
     if flag.startswith('-I'):
       # Relative paths need to be resolved, because they're relative to the
       # output dir, not the source.
       if flag[2] == '/':
         chrome_flags.append(flag)
       else:
         abs_path = os.path.normpath(os.path.join(out_dir, flag[2:]))
         chrome_flags.append('-I' + abs_path)
+    elif flag.startswith('-std'):
+      chrome_flags.append(flag)
     elif flag.startswith('-') and flag[1] in 'DWFfmO':
       if flag == '-Wno-deprecated-register' or flag == '-Wno-header-guard':
         # These flags causes libclang (3.3) to crash. Remove it until things
         # are fixed.
         continue
       chrome_flags.append(flag)
 
   return chrome_flags
 
 
@@ skipping 10 matching lines @@
   """
   chrome_root = FindChromeSrcFromFilename(filename)
   chrome_flags = GetClangCommandFromNinjaForFilename(chrome_root,
                                                      filename)
   final_flags = flags + chrome_flags
 
   return {
     'flags': final_flags,
     'do_cache': True
   }