Introduces the timeout of app_list search.

It would be great to select the first item automatically when
the search happen through speech recognition. This CL does
the following things:
- Adds timeout to AppListViewDelegate
- It is an open ended question that who should handle the
  actual timeout and its progress. Because the timeout indicator
  animation should be platform-dependant, I think it's better
  to handle inside of views
- Timeout is a static value right now, just 3 secs, this
  should be changed later.
- Timeout indicator UI is not fixed. We should discuss
  this on the issue.

BUG=334284
R=xiyuan@chromium.org
TBR=oshima@chromium.org
TEST=manually

Review URL: https://codereview.chromium.org/140813004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246815 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246815