Abstracted AcceptPasswordAutofillSuggestion IPC out of core Autofill code.

BUG=302479

Review URL: https://codereview.chromium.org/79103002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236768 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236768