Add option to allow mojob to specify extra gn args.

mojo/tools/mopy/gn.py

 # Copyright 2015 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.
 
 """
 GN-related configuration functions, e.g., to produce a Config object from a GN
 args.gn file).
 """
 
 
@@ skipping 56 matching lines @@
     gn_args["use_glib"] = False
     gn_args["use_system_harfbuzz"] = False
   elif config.target_os == Config.OS_LINUX:
     gn_args["is_desktop_linux"] = False
     gn_args["use_aura"] = False
     gn_args["use_glib"] = False
     gn_args["use_system_harfbuzz"] = False
 
   gn_args["target_cpu"] = config.target_cpu
 
+  extra_args = config.values.get("gn_args")
+  if extra_args:
+    for arg in extra_args.split():
+      (name, val) = arg.split('=')
+      gn_args[name] = val
+
   return gn_args
 
 
 def CommandLineForGNArgs(gn_args):
   """
   Returns the list of gn arguments to use with the gn command line.
   """
   def _ToCommandLine(key, value):
     if type(value) is bool:
       return "%s=%s" % (key, "true" if value else "false")
@@ skipping 34 matching lines @@
   values = {}
   with open(gn_file, "r") as f:
     for line in f.readlines():
       line = re.sub("\s*#.*", "", line)
       result = re.match("^\s*(\w+)\s*=\s*(.*)\s*$", line)
       if result:
         key = result.group(1)
         value = result.group(2)
         values[key] = ast.literal_eval(TRANSLATIONS.get(value, value))
   return values