Reload Instant NTP and Instant-process tabs on search url change

. Add a default impl of instant_service_observer.

. Move pref change listener for default search provider to
instant_service and pass to browser_instant_controller and
instant_ntp_prerenderer via instant_service_observer.

. Add a search-domain-check listener to instant_service in a similar
manner.

. Replaced ReloadStaleNTP, PreloadInstantNTP etc with ReloadInstantNTP

. Introduce InstantUnitTestBase
  - InstantServiceTest and BrowserInstantControllerTest are subclasses.

. InstantService Unit Test
  - Use a mock observer to verify the search provider change and 
    google url update is triggered on observers.
  - Verify the prerendered NTP is reloaded.

. BrowserInstantController Unit Test
  - Moved the tab reload test from interactive ui test to 
     BrowserInstantControllerTest.


R=jered@chromium.org, samarth@chromium.org
TBR=sky@chromium.org
BUG=254206

Review URL: https://chromiumcodereview.appspot.com/20388003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225063 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225063