Renable PrerenderBrowserTest.PrerenderDelayLoadPlugin on Windows and other platforms that it was enabled on. r228305 disabled it on all platforms even though it was flaking just on Linux.

Also enable PrerenderIframeDelayLoadPlugin on Win Aura since plugins work there now.

BUG=306715,103496
R=abodenha@chromium.org

Review URL: https://codereview.chromium.org/101633004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239584 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239584