Handle <link rel=prerender> in chrome.

chrome/renderer/page_load_histograms.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/renderer/page_load_histograms.h"
 
 #include "base/logging.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/time.h"
@@ skipping 288 matching lines @@
         PLT_HISTOGRAM(base::FieldTrial::MakeName(
             "PLT.BeginToFinish_LinkLoadStaleOk", "DnsImpact"),
             begin_to_finish_all_loads);
         break;
       default:
         break;
     }
   }
 
   // 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) {
     if (navigation_state->was_prefetcher()) {
       PLT_HISTOGRAM(base::FieldTrial::MakeName(
           "PLT.BeginToFinishDoc_ContentPrefetcher", "Prefetch"),
           begin_to_finish_doc);
       PLT_HISTOGRAM(base::FieldTrial::MakeName(
           "PLT.BeginToFinish_ContentPrefetcher", "Prefetch"),
           begin_to_finish_all_loads);
@@ skipping 501 matching lines @@
 
   DCHECK(state);
   DCHECK(ds);
   GURL url(ds->request().url());
   Time start = state->start_load_time();
   Time finish = state->finish_load_time();
   // TODO(mbelshe): should we log more stats?
   VLOG(1) << "PLT: " << (finish - start).InMilliseconds() << "ms "
           << url.spec();
 }