Ensure build fails if Observatory fails to build

tools/observatory_tool.py

 #!/usr/bin/env python
 # Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 """Helper for building and deploying Observatory"""
 
 import argparse
 import os
 import shutil
 import subprocess
@@ skipping 50 matching lines @@
                           output_dir])
 
 def Deploy(input_dir, output_dir):
   shutil.rmtree(output_dir)
   shutil.copytree(input_dir, output_dir, ignore=IGNORE_PATTERNS)
   return 0
 
 def ExecuteCommand(options, args):
   cmd = options.command
   if (cmd == 'get'):
-    PubGet(options.dart_executable, options.package_root)
+    return PubGet(options.dart_executable, options.package_root)
   elif (cmd == 'build'):
-    PubBuild(options.dart_executable, options.package_root, args[0])
+    return PubBuild(options.dart_executable, options.package_root, args[0])
   elif (cmd == 'deploy'):
     Deploy('build', 'deployed')
   else:
     print >> sys.stderr, ('ERROR: command "%s" not supported') % (cmd)
     return -1;
 
 def main():
   # Parse the options.
   parser = BuildArguments()
   (options, args) = parser.parse_known_args()
   if not ProcessOptions(options, args):
     parser.print_help()
     return 1
   if os.getenv('DART_USE_BOOTSTRAP_BIN') != None:
     dart_executable = options.dart_executable
   # Calculate absolute paths before changing directory.
   options.package_root = os.path.abspath(options.package_root)
   options.dart_executable = os.path.abspath(options.dart_executable)
   if len(args) == 1:
     args[0] = os.path.abspath(args[0])
   # Pub must be run from the project's root directory.
   ChangeDirectory(options.directory)
   return ExecuteCommand(options, args)
 
 if __name__ == '__main__':
   sys.exit(main());