Add support for Mac vs. Linux sky_server builds

sky/tools/test_perf

 #!/usr/bin/env python
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from skypy.find_tests import find_tests
 from skypy.paths import Paths
 import argparse
 import os
 import re
 import requests
 import skypy.configuration as configuration
+import skypy.skyserver
 import subprocess
 
 
 SUPPORTED_MIME_TYPES = [
     'text/html',
     'text/sky',
     'text/plain',
 ]
 HTTP_PORT = 9999
 URL_ROOT = 'http://localhost:%s/' % HTTP_PORT
@@ skipping 39 matching lines @@
     requests.post(DASHBOARD_URL, params={ 'data': json })
 
 
 class PerfHarness(object):
     def __init__(self, args):
         self._sky_server = None
         self.paths = Paths(os.path.join('out', 'Debug'))
         self.args = args
 
     def _start_server(self):
-        subprocess.call(os.path.join(self.paths.sky_tools_directory,
-            'download_sky_server'))
+        # TODO(eseidel): Shouldn't this just use skyserver.py?
         return subprocess.Popen([
-            os.path.join(self.paths.src_root, 'out', 'downloads', 'sky_server'),
+            SkyServer.sky_server_path(),
             self.paths.src_root,
             str(HTTP_PORT),
             '-t', self.args.configuration
         ])
 
     def _sky_tester_command(self, url):
         content_handlers = ['%s,%s' % (mime_type, 'mojo:sky_viewer')
             for mime_type in SUPPORTED_MIME_TYPES]
         return [
             self.paths.mojo_shell_path,
@@ skipping 36 matching lines @@
     try:
         harness.main()
     except (KeyboardInterrupt, SystemExit):
         pass
     finally:
         harness.shutdown()
 
 
 if __name__ == '__main__':
     main()