Convert editing/style/style-3998892-fix.html to use w3c test harness

This patch converts "editing/style/style-3998892-fix.html" to use w3c test
harness to simplify test files.

This patch is a preparation of getting rid of grammar checking feature.

BUG=619452
TEST=n/a; this patch changes a test file

Review-Url: https://codereview.chromium.org/2183763003
Cr-Commit-Position: refs/heads/master@{#408016}
7 files changed