Update line height when changing multiplier.

Line height is cached in the RenderBlock; when FTA updates a multiplier it needs to force recomputation of the line height.

(The old autosizer avoids this issue by using setStyle instead of setStyleInternal.  This triggers style recalc, which invalidates the line height.)

BUG=353309,354032

Review URL: https://codereview.chromium.org/209853007

git-svn-id: svn://svn.chromium.org/blink/trunk@169975 bbb929c8-8fbe-4397-9dbb-9b2b20218538