Fuchsia: Adds a script to download the prebuilt SDK

tools/download_prebuilt_sdk.py

Index: tools/download_prebuilt_sdk.py
diff --git a/tools/download_prebuilt_sdk.py b/tools/download_prebuilt_sdk.py
new file mode 100755
index 0000000000000000000000000000000000000000..f3c43853347aaff7d3f8e6f513109b28809e6853
--- /dev/null
+++ b/tools/download_prebuilt_sdk.py
@@ -0,0 +1,52 @@
+#!/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 os
+import subprocess
+import sys
+import tarfile
+import urllib
+import utils
+
+HOST_OS = utils.GuessOS()
+HOST_ARCH = utils.GuessArchitecture()
+SCRIPT_DIR = os.path.dirname(sys.argv[0])
+DART_ROOT = os.path.realpath(os.path.join(SCRIPT_DIR, '..'))
+
+BUCKET_NAME = 'dart-dependencies'
+
+def host_os_for_sdk(host_os):
+  if host_os.startswith('macos'):
+    return 'mac'
+  if host_os.startswith('win'):
+    return 'win'
+  return host_os
+
+def main(argv):
+  host_os = host_os_for_sdk(HOST_OS)
+  sdk_path = os.path.join(DART_ROOT, 'tools', 'sdks', host_os)
+  stamp_path = os.path.join(sdk_path, 'dart-sdk.tar.gz.stamp')
+  sha_path = os.path.join(sdk_path, 'dart-sdk.tar.gz.sha1')
+  tgz_path = os.path.join(sdk_path, 'dart-sdk.tar.gz')
+
+  stamp = ''
+  if os.path.isfile(stamp_path):
+    with open(stamp_path, 'r') as fp:
+      stamp = fp.read()
+
+  with open(sha_path, 'r') as fp:
+    sha = fp.read()
+
+  if stamp != sha:
+    url = ('https://%s.storage.googleapis.com/%s' % (BUCKET_NAME, sha))
+    print 'Downloading prebuilt Dart SDK from: ' + url
+    urllib.urlretrieve(url, tgz_path)
+    with tarfile.open(tgz_path) as tar:
+      tar.extractall(sdk_path)
+    with open(stamp_path, 'w') as fp:
+      fp.write(sha)
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv))