[Autofill] Reduce Autofill-generated IPC spam.

Along the way, update some names to be shorter and clearer.

BUG=343322
TEST=fewer unnecessary IPC messages.
R=estade@chromium.org

Review URL: https://codereview.chromium.org/176253002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253150 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253150