Change defaults for build args to accommodate Flutter and Fuchsia.

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 shutil
 import subprocess
@@ skipping 205 matching lines @@
 
   dont_use_clang = DontUseClang(args, gn_args['target_os'],
                                       gn_args['host_cpu'],
                                       gn_args['target_cpu'])
   gn_args['is_clang'] = args.clang and not dont_use_clang
 
   gn_args['is_asan'] = args.asan and gn_args['is_clang']
   gn_args['is_msan'] = args.msan and gn_args['is_clang']
   gn_args['is_tsan'] = args.tsan and gn_args['is_clang']
 
-  gn_args['dart_platform_sdk'] = args.platform_sdk
+  if not args.platform_sdk and not gn_args['target_cpu'].startswith('arm'):
+    gn_args['dart_platform_sdk'] = args.platform_sdk
+  gn_args['dart_stripped_binary'] = 'exe.stripped/dart'
 
   # Setup the user-defined sysroot.
   if gn_args['target_os'] == 'linux' and args.wheezy and not crossbuild:
     gn_args['dart_use_wheezy_sysroot'] = True
   else:
     sysroot = TargetSysroot(args)
     if sysroot:
       gn_args['target_sysroot'] = ParseStringMap(arch, sysroot)
 
     toolchain = ToolchainPrefix(args)
@@ skipping 248 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))