Modifications to the layout test framework so that it can use browser_tests as a
driver. This is for end to end testing for print preview.
BUG=388517

Review URL: https://codereview.chromium.org/401883007

git-svn-id: svn://svn.chromium.org/blink/trunk@178511 bbb929c8-8fbe-4397-9dbb-9b2b20218538