Remove ClosedCaptionEdgeAttribute, ClosedCaptionFont & Flags enum

Replace enum with some non-used code (for example saving flags with Font info or using non-standard CSS values when generating CSS info for font) with functions. Additionally there are removed some non-necessary tests.

BUG=919666

Change-Id: Icee429a735358e8409bc4792db72dcafd6acc5ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1548475
Reviewed-by: Katie Dektar <katie@chromium.org>
Commit-Queue: Marcin Wiącek <marcin@mwiacek.com>
Cr-Commit-Position: refs/heads/master@{#654974}