Convert extend-by-character-[1-6].html to use assert_selection
This patch converts "extend-by-character-[1-6].html" in "editing/selection" to
use |assert_selection()| test harness to simplify test files and consolidate
into "extend_by_character.html" to run tests faster.
This patch is a preparation of getting rid of grammar checking feature.
BUG=
619452
TEST=n/a; this patch changes a test file
Committed:
https://crrev.com/2b0ece62b99aeb105a26423d1d0390c722b4fef3
Cr-Commit-Position: refs/heads/master@{#408319}