This makes it possible to effectively re-route the stdout by
re-assigning sys.stdout.

BUG=

Review URL: https://codereview.chromium.org/303223005

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@273595 0039d316-1c4b-4281-b951-d872f2087c98