Text Match Highlight

Based on svg/custom/text-match-highlight.html. Here run it as a repaint test to check correctness of invalidation.
Automatic test requires run-layout-test. To manually test, open this file in Chrome and find 'findme' in the page.
There should be 9 highlighted instances of "findme". The 6th higlighted instance should be active.

Lorum ipsum findme lorum ipsum findmefindme lorum.
longtextfindmenoyou.
Can you findme in this boring text?Findme in a typewriter! Findme on a path! Did you findme?