aura: Updates the text input client when native activation changes.
It turned out that we should update the focused text input client not only when native focus/blur but also when native activate/deactivate.
See crbug.com/377479 for details.
Also this CL fixes the initial text input focus on CrOS login screen.
BUG=323376,290701
TEST=Confirmed that the Omnibox gets the text input focus by default when a new window is created.
Review URL: https://codereview.chromium.org/
294023002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276437 0039d316-1c4b-4281-b951-d872f2087c98