Componentize AutofillManager unittest.

- Removes usage of ChromeRenderViewHostTestHarness
- Replaces usage of TabAutofillManagerDelegate with TestAutofillManagerDelegate
- Replaces usage of content::MessageLoopRunner with base::RunLoop

BUG=303083
R=joi@chromium.org

Review URL: https://codereview.chromium.org/187463004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255034 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255034