Support whole-word search in FindBuffer

This CL makes FindBuffer able to filter out non-whole-word find results
if needed. So on the text "foo foobar", there is only 1 match for "foo"
and 0 match for "bar".

Bug: 868227
Change-Id: Iaf31fb71c4b345a71061e6957ecd60f302de930e
Reviewed-on: https://chromium-review.googlesource.com/c/1445354
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628280}
7 files changed