Prevent excessive beeping in case of Find On Page search failure

Prevent excessive beeping in case of Find On Page search failure

Previously, Chrome would beep when updating the find on page result count if a
frame was added or removed from the page and there were no search matches. Now
Chrome will only beep in response to a user's query failing to find results in
the frames of the page at the time of the initial query. Subsequent addition or
removal of frames will still update the result counter.

BUG=682299