New search behavior for empty query

It's a very lightweight change to implment the new spec, which says:
- Don't start searching until the user types the first letter
- But if the search view is shown, make the ALL tab current, and disable swipe

With this CL,
- No changes to ActionBarAdapter.isSearchMode().  It still returns true
  if the search view is visible, even if it's empty.
- However, in order to make the all fragment show the normal list for
  empty query, only turn the fragment into the search mode if the query is
  non-empty.

Also reverts I25908651 as we no longer do a search with empty query.

Bug 5104010

Change-Id: I50038994c6d65aab71ceefdf9218f3c7ad2bc6a4