Add support for configurable -OX optimization levels for debug builds

tools/gn.py

 #!/usr/bin/env python
 # Copyright 2016 The Dart project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import argparse
 import multiprocessing
 import os
 import subprocess
 import sys
@@ skipping 184 matching lines @@
   if args.goma and goma_dir:
     gn_args['use_goma'] = True
     gn_args['goma_dir'] = goma_dir
   elif args.goma and os.path.exists(goma_home_dir):
     gn_args['use_goma'] = True
     gn_args['goma_dir'] = goma_home_dir
   else:
     gn_args['use_goma'] = False
     gn_args['goma_dir'] = None
 
+  gn_args['dart_debug_optimization_level'] = args.debug_opt_level
+
   return gn_args
 
 
 def process_os_option(os_name):
   if os_name == 'host':
     return HOST_OS
   return os_name
 
 
 def process_options(args):
@@ skipping 84 matching lines @@
       default=use_asan(),
       action='store_true')
   other_group.add_argument('--no-asan',
       help='Disable ASAN',
       dest='asan',
       action='store_false')
   other_group.add_argument('--clang',
       help='Use Clang',
       default=True,
       action='store_true')
+  other_group.add_argument('--debug-opt-level',
+      '-d',
+      help='The optimization level to use for debug builds',
+      type=int,
+      default=2)
   other_group.add_argument('--no-clang',
       help='Disable Clang',
       dest='clang',
       action='store_false')
   other_group.add_argument('--goma',
       help='Use goma',
       default=True,
       action='store_true')
   other_group.add_argument('--no-goma',
       help='Disable goma',
@@ skipping 97 matching lines @@
       return 1
 
   endtime = time.time()
   if args.verbose:
     print ("GN Time: %.3f seconds" % (endtime - starttime))
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))