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 void SetUp() {
    SafeBrowsingService::RegisterFactory(&factory_);
    SafeBrowsingBlockingPage::RegisterFactory(&blocking_page_factory_);
    MalwareDetails::RegisterFactory(&details_factory_);
    InProcessBrowserTest::SetUp();
  }

  virtual void SetUp() {
    SafeBrowsingService::RegisterFactory(&factory_);
    SafeBrowsingBlockingPage::RegisterFactory(&blocking_page_factory_);
    MalwareDetails::RegisterFactory(&details_factory_);
    InProcessBrowserTest::SetUp();
  }
