The syntax is:
deps {
  'path': File('http://svn..../path/file@42')
}

This will checkout a single file and use scm.update to
keep it up to date.

See https://bugs.webkit.org/show_bug.cgi?id=36578#c7 for a
description of why I want to add this.

Review URL: http://codereview.chromium.org/1356005

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@43911 0039d316-1c4b-4281-b951-d872f2087c98