[infra] Make gclient runhooks gn for Android on supported platforms

tools/generate_buildfiles.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 os
 import subprocess
 import sys
 import utils
 
+HOST_OS = utils.GuessOS()
 SCRIPT_DIR = os.path.dirname(sys.argv[0])
 DART_ROOT = os.path.realpath(os.path.join(SCRIPT_DIR, '..'))
 DART_USE_GYP = "DART_USE_GYP"
 DART_DISABLE_BUILDFILES = "DART_DISABLE_BUILDFILES"
 
 
 def use_gyp():
   return DART_USE_GYP in os.environ
 
 
 def disable_buildfiles():
   return DART_DISABLE_BUILDFILES in os.environ
 
 
 def execute(args):
   process = subprocess.Popen(args, cwd=DART_ROOT)
   process.wait()
   return process.returncode
 
 
-def run_gn(options):
+def run_android_gn(options):
+  if not HOST_OS in ['linux', 'macos']:
+    return 0
   gn_command = [
     'python',
     os.path.join(DART_ROOT, 'tools', 'gn.py'),
+    '-m', 'all',
+    '-a', 'arm,arm64',
+    '--os', 'android',
+  ]
+  if options.verbose:
+    gn_command.append('-v')
+    print ' '.join(gn_command)
+  return execute(gn_command)
+
+
+def run_host_gn(options):
+  gn_command = [
+    'python',
+    os.path.join(DART_ROOT, 'tools', 'gn.py'),
     '-m', 'all',
     '-a', 'all',
   ]
   if options.verbose:
     gn_command.append('-v')
     print ' '.join(gn_command)
   return execute(gn_command)
 
 
+def run_gn(options):
+  status = run_host_gn(options)
+  if status != 0:
+    return status
+  return run_android_gn(options)
+
+
 def run_gyp(options):
   gyp_command = [
     'python',
     os.path.join(DART_ROOT, 'tools', 'gyp_dart.py'),
   ]
   if options.verbose:
     print ' '.join(gyp_command)
   return execute(gyp_command)
 
 
@@ skipping 28 matching lines @@
     return 0
   options = parse_args(argv)
   if options.gn:
     return run_gn(options)
   else:
     return run_gyp(options)
 
 
 if __name__ == '__main__':
     sys.exit(main(sys.argv))