make StackingClient dispatch to either ash or desktop

chrome/browser/prerender/prerender_manager.cc

Index: chrome/browser/prerender/prerender_manager.cc
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index 5e7d093cd15ffcf57107c7dede0bb9e40dc55ad6..c4169d8721311825d079e0d9cf81edc86b79f92c 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -236,6 +236,10 @@ PrerenderHandle* PrerenderManager::AddPrerenderFromLinkRelPrerender(
   // TODO(jcivelli): http://crbug.com/113322 We should have an option to disable
   //                link-prerender and enable omnibox-prerender only.
   return NULL;
+#elif defined(OS_WIN) && defined(USE_AURA)
+  // TODO(scottmg): http://crbug.com/128578 WebContentsViewAura can't get a
+  // valid parent window here.
+  return NULL;
 #else
   DCHECK(!size.IsEmpty());
   Origin origin = ORIGIN_LINK_REL_PRERENDER_CROSSDOMAIN;