Modifications to layout test framework so that it can work with browsertests. This is for end to end testing for print preview.

BUG=388517

Review URL: https://codereview.chromium.org/378113003

git-svn-id: svn://svn.chromium.org/blink/trunk@178486 bbb929c8-8fbe-4397-9dbb-9b2b20218538