Web Animations: Support animation of line-height

BUG=257591

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=161022

Review URL: https://codereview.chromium.org/26492005

git-svn-id: svn://svn.chromium.org/blink/trunk@161242 bbb929c8-8fbe-4397-9dbb-9b2b20218538