Add one-time randomization support for FieldTrial, and the ability to

chrome/renderer/prerender/prerender_helper.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/prerender/prerender_helper.h"
 
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "chrome/common/render_messages.h"
 #include "content/renderer/navigation_state.h"
@@ skipping 27 matching lines @@
   PrerenderHelper* prerender_helper = PrerenderHelper::Get(render_view);
   return (prerender_helper && prerender_helper->is_prerendering_);
 }
 
 // static.
 void PrerenderHelper::RecordHistograms(
     RenderView* render_view,
     const base::Time& finish_all_loads,
     const base::TimeDelta& begin_to_finish_all_loads) {
   static bool use_prerender_histogram =
-      base::FieldTrialList::Find("Prefetch") &&
-      !base::FieldTrialList::Find("Prefetch")->group_name().empty();
+      base::FieldTrialList::TrialExists("Prefetch");
   if (!use_prerender_histogram)
     return;
 
   PrerenderHelper* prerender_helper = PrerenderHelper::Get(render_view);
 
   // Load time for non-prerendered pages.
   if (!prerender_helper) {
     RECORD_PLT("RendererPerceivedPLT", begin_to_finish_all_loads);
     return;
   }
@@ skipping 95 matching lines @@
 
   is_prerendering_ = false;
   prerender_display_time_ = base::Time::Now();
 }
 
 bool PrerenderHelper::HasUnrecordedData() const {
   return !prerender_display_time_.is_null();
 }
 
 }  // namespace prerender