Handling new frames and frame navigations with find-in-page during a find session.

This patch implements new find-in-page functionality that allows for frames that are either newly added or navigated during a find session to be automatically searched so that matches in their new content are automatically highlighted and included in the results shown in the find bar.

Also, there is a fix included in this patch to prevent the find-in-page bar from closing when a subframe navigates (the find session should only end if the main frame navigates).

Design doc: https://docs.google.com/document/d/1r4F19FIKg4zPJCaSyJ9-T0sgFbxlCGKL3FjqQEAKegg/view

BUG=2220,621660

Review-Url: https://codereview.chromium.org/2236403004
Cr-Commit-Position: refs/heads/master@{#420715}
9 files changed