Remove TabContents from TabStripModelObserver::TabDetachedAt.

BUG=107201
TEST=no visible change


Review URL: https://chromiumcodereview.appspot.com/11293205

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@167122 0039d316-1c4b-4281-b951-d872f2087c98
WebContents* TabStripModel::GetWebContentsAtImpl(int index) const {
  CHECK(ContainsIndex(index)) <<
      "Failed to find: " << index << " in: " << count() << " entries.";
  return contents_data_[index]->contents;
}

WebContents* TabStripModel::GetWebContentsAtImpl(int index) const {
  CHECK(ContainsIndex(index)) <<
      "Failed to find: " << index << " in: " << count() << " entries.";
  return contents_data_[index]->contents;
}
