CHROME_HEADLESS is always Pro

Follow up to https://codereview.chromium.org/185423004/

The unzip is always Pro, and without setting this the data.json will
be getting the Express settings and so gyp will generate the wrong
project.

TBR=iannucci@chromium.org
BUG=323300

Review URL: https://codereview.chromium.org/188673003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@255378 0039d316-1c4b-4281-b951-d872f2087c98

win_toolchain/toolchain2013.py

@@ -465,6 +465,7 @@ def main():
     # correctly, as we don't otherwise care about working directory.
     os.chdir(os.path.join(BASEDIR, '7z'))
     if options.bot_mode and options.sha1:
+      options.express = False
       DoTreeMirror(target_dir, options.sha1)
     else:
       images = GetSourceImages(options.local, not options.express)