Don't delete the current NavigationEntry when leaving an interstitial page.

BUG=107182
TEST=See bug

Review URL: http://codereview.chromium.org/8976014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@115189 0039d316-1c4b-4281-b951-d872f2087c98
  virtual bool CheckBrowseUrl(const GURL& gurl, Client* client) {
    if (badurls[gurl.spec()] == SAFE)
      return true;

    BrowserThread::PostTask(
        BrowserThread::IO, FROM_HERE,
        base::Bind(&FakeSafeBrowsingService::OnCheckBrowseURLDone,
                   this, gurl, client));
    return false;
  }

  virtual bool CheckBrowseUrl(const GURL& gurl, Client* client) {
    if (badurls[gurl.spec()] == SAFE)
      return true;

    BrowserThread::PostTask(
        BrowserThread::IO, FROM_HERE,
        base::Bind(&FakeSafeBrowsingService::OnCheckBrowseURLDone,
                   this, gurl, client));
    return false;
  }
