Re-enable prerender client redirect tests.

Re-enabling
  PrerenderBrowserTest.PrerenderClientRedirectNavigateToFirst
  PrerenderBrowserTest.PrerenderClientRedirectNavigateToSecondViaClick
  PrerenderBrowserTest.PrerenderClientRedirectInIframe

With all the changes to the tests lately, let's re-enable them unless they
start flaking again.

BUG=249179

Review URL: https://codereview.chromium.org/155163002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249261 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249261