Kill NavigationControllerBase. I merged the two into NavigationController.

      This fixes a leak of NavigationEntry's by using the spiffy linked ptr. I had to
add a const to linked_ptr for the comparisons to work.

BUG=1319484

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@1137 0039d316-1c4b-4281-b951-d872f2087c98