GitLab

 - Place stray calls to chrome.send() and cr.sendWithPromise() in
   c/b/r/settings/chromeos/date_time_page/ behind a browser proxy.
 - Update date_time_page_tests.js to leverage TestBrowserProxy.
 - Remove any calls to the obsolete registerMessageCallback() test
   helper, as well as any setTimeout() calls in
   date_time_page_tests.js.

This cleanup also revealed a completely defunct test case
"set date and time button", where no code in the test was actually
executed (also fixed).

The motivation behind this is to remove usages of
registerMessageCallback() test helper in order to eventually fully
remove it.

Bug: 1148403,1147940
Change-Id: I786cb2485483c7477bd6fd746cd3f1a054be4d3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532674Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: dpapad <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826923}