Add NavigationToFirstContentfulPaint UMA for ServiceWorker controlled pages.

components/page_load_metrics/renderer/metrics_render_frame_observer.cc

 // Copyright 2015 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 "components/page_load_metrics/renderer/metrics_render_frame_observer.h"
 
 #include <string>
 
 #include "base/time/time.h"
 #include "base/timer/timer.h"
@@ skipping 91 matching lines @@
   return true;
 }
 
 PageLoadTiming MetricsRenderFrameObserver::GetTiming() const {
   const blink::WebPerformance& perf =
       render_frame()->GetWebFrame()->performance();
 
   PageLoadTiming timing;
   double start = perf.navigationStart();
   timing.navigation_start = base::Time::FromDoubleT(start);
+  timing.worker_start = base::Time::FromDoubleT(perf.workerStart());
   timing.response_start = ClampDelta(perf.responseStart(), start);
   timing.dom_loading = ClampDelta(perf.domLoading(), start);
   timing.dom_content_loaded_event_start =
       ClampDelta(perf.domContentLoadedEventStart(), start);
   timing.load_event_start = ClampDelta(perf.loadEventStart(), start);
   timing.first_layout = ClampDelta(perf.firstLayout(), start);
   timing.first_paint = ClampDelta(perf.firstPaint(), start);
   timing.first_text_paint = ClampDelta(perf.firstTextPaint(), start);
   timing.first_image_paint = ClampDelta(perf.firstImagePaint(), start);
   timing.first_contentful_paint =
@@ skipping 12 matching lines @@
   return make_scoped_ptr(new base::OneShotTimer);
 }
 
 bool MetricsRenderFrameObserver::HasNoRenderFrame() const {
   bool no_frame = !render_frame() || !render_frame()->GetWebFrame();
   DCHECK(!no_frame);
   return no_frame;
 }
 
 }  // namespace page_load_metrics