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
void AllDownloadsCompleteObserver::ManagerGoingDown(DownloadManager* manager) {
  DCHECK_EQ(manager, download_manager_);
  download_manager_->RemoveObserver(this);
  download_manager_ = NULL;
}

void AllDownloadsCompleteObserver::ManagerGoingDown(DownloadManager* manager) {
  DCHECK_EQ(manager, download_manager_);
  download_manager_->RemoveObserver(this);
  download_manager_ = NULL;
}
