Handle <link rel=prerender> in chrome.

chrome/renderer/page_load_histograms.cc

Index: chrome/renderer/page_load_histograms.cc
diff --git a/chrome/renderer/page_load_histograms.cc b/chrome/renderer/page_load_histograms.cc
index 84365e8a460297832c44c88ecfd4bd68c736aab1..5581afa387f51bc339c5dfb7d6f110389ec88c65 100644
--- a/chrome/renderer/page_load_histograms.cc
+++ b/chrome/renderer/page_load_histograms.cc
@@ -306,6 +306,9 @@ void PageLoadHistograms::Dump(WebFrame* frame) {
   }
 
   // Histograms to determine if content prefetching has an impact on PLT.
+  // TODO(gavinp): Right now the prerendering and the prefetching field trials
+  // are mixed together.  If we continue to launch prerender with
+  // link rel=prerender, then we should separate them.
   static const bool prefetching_fieldtrial =
       base::FieldTrialList::TrialExists("Prefetch");
   if (prefetching_fieldtrial) {