Omnibox: Clear SearchProvider Cache On Input & Invalid Inputs

BUG=344217
R=pkasting@chromium.org

Review URL: https://codereview.chromium.org/178803003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253288 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253288