Fix search in hidden subframes.

* Change way of determining if frame has visible content. Subframe lookups in style of ownerRenderer. 

BUG=367141

Review URL: https://codereview.chromium.org/256683005

git-svn-id: svn://svn.chromium.org/blink/trunk@173291 bbb929c8-8fbe-4397-9dbb-9b2b20218538