Make "official build" not the default, if is_official_build is not set in 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 87 matching lines @@
   return [_ToCommandLine(x, y) for x, y in gn_args.iteritems()]
 
 
 def ConfigForGNArgs(args):
   """
   Return the Config object for the given gn arguments. This function takes a
   dictionary with boolean values as boolean.
   """
   config_args = {}
   config_args["is_debug"] = args.get("is_debug", True)
-  config_args["is_official_build"] = args.get("is_official_build", True)
+  config_args["is_official_build"] = args.get("is_official_build", False)
   config_args["sanitizer"] = (
       Config.SANITIZER_ASAN if args.get("is_asan") else None)
   config_args["is_clang"] = args.get("is_clang", False)
   config_args["use_goma"] = args.get("use_goma", False)
   if config_args["use_goma"]:
     config_args["goma_dir"] = args.get("goma_dir")
   config_args["use_nacl"] = args.get("mojo_use_nacl", False)
   config_args["mojo_use_go"] = args.get("mojo_use_go", False)
   if config_args["mojo_use_go"]:
     config_args["go_build_tool"] = args.get("go_build_tool")
@@ skipping 16 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