[Sheriffing] Reenable PrerenderBrowserTestWithNaCl.PrerenderNaClPluginEnabled test.
[Sheriffing] Reenable PrerenderBrowserTestWithNaCl.PrerenderNaClPluginEnabled test.

TBR=mmenke@chromium.org,svaldez@chromium.org
BUG=569221

Review URL: https://codereview.chromium.org/1588063004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#369742}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk