Ultimately, I think we'd want to let the user blur the dialog without clearing highlights (and without closing the Find bar) -- which is allowed in Chrome and several code editors (Sublime, WebStorm/IntelliJ, ...).

I think the value of match highlighting is reduced if you can't interact with the text at all while the highlights are visible.  But doing it this way _does_ duck some thorny issues: what to do if edits create/destroy matching text while highlighting is on.  So I actually think this patch is a reasonable way to incrementally deliver some value.

(And there's at least one popular editor that does match highlighting but clears is as soon as you blur the Find bar: Espresso).