spellcheck-disable-enable.html fails when asynchronous spellchecking is on

This test doesn't need asynchronous spell checking.
Its purpose is to verify how spelling markers behave when
spell checker feature is being toggled.

Restore synchronous spell checking which was disabled at r157059
and remove unnecessary and misleading code.

BUG=282426

Review URL: https://chromiumcodereview.appspot.com/23530023

git-svn-id: svn://svn.chromium.org/blink/trunk@157229 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: The editor now has red background color when changes made are at risk of loss.

Drive-by: Fix this behavior for restored revisions.

BUG=285150

Review URL: https://chromiumcodereview.appspot.com/23530024

git-svn-id: svn://svn.chromium.org/blink/trunk@157230 bbb929c8-8fbe-4397-9dbb-9b2b20218538