[chromedriver] When archiving, upload a latest file that points to it.

chrome/test/chromedriver/run_buildbot_steps.py

Index: chrome/test/chromedriver/run_buildbot_steps.py
diff --git a/chrome/test/chromedriver/run_buildbot_steps.py b/chrome/test/chromedriver/run_buildbot_steps.py
index 85fdb10b99a38a8ef6432b8f944b95426407e39e..f4e2e1b211fc9a35370042ec346cc953d4d0bf5f 100755
--- a/chrome/test/chromedriver/run_buildbot_steps.py
+++ b/chrome/test/chromedriver/run_buildbot_steps.py
@@ -195,11 +195,20 @@ def _ArchiveGoodBuild(platform, revision):
   zip_path = util.Zip(os.path.join(chrome_paths.GetBuildDir([server_name]),
                                    server_name))
 
-  build_url = '%s/chromedriver_%s_%s.%s.zip' % (
-      GS_CONTINUOUS_URL, platform, _GetVersion(), revision)
+  build_name = 'chromedriver_%s_%s.%s.zip' % (
+      platform, _GetVersion(), revision)
+  build_url = '%s/%s' % (GS_CONTINUOUS_URL, build_name)
   if slave_utils.GSUtilCopy(zip_path, build_url):
     util.MarkBuildStepError()
 
+  (latest_fd, latest_file) = tempfile.mkstemp()
+  os.write(latest_fd, build_name)
+  os.close(latest_fd)
+  latest_url = '%s/latest_%s' % (GS_CONTINUOUS_URL, platform)
+  if slave_utils.GSUtilCopy(latest_file, latest_url, mimetype='text/plain'):
+    util.MarkBuildStepError()
+  os.remove(latest_file)
+
 
 def _MaybeRelease(platform):
   """Releases a release candidate if conditions are right."""