Add CSSTiming to collect aggregate PLT-level stats about CSS.

chrome/renderer/page_load_metrics/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 "chrome/renderer/page_load_metrics/metrics_render_frame_observer.h"
 
 #include <string>
 
 #include "base/memory/ptr_util.h"
 #include "base/time/time.h"
@@ skipping 126 matching lines @@
     timing.parse_blocked_on_script_load_from_document_write_duration =
         base::TimeDelta::FromSecondsD(
             perf.parseBlockedOnScriptLoadFromDocumentWriteDuration());
     timing.parse_blocked_on_script_execution_duration =
         base::TimeDelta::FromSecondsD(
             perf.parseBlockedOnScriptExecutionDuration());
     timing.parse_blocked_on_script_execution_from_document_write_duration =
         base::TimeDelta::FromSecondsD(
             perf.parseBlockedOnScriptExecutionFromDocumentWriteDuration());
   }
+
+  if (perf.authorStyleSheetParseDurationBeforeFCP() > 0.0) {
+    timing.style_sheet_timing.author_style_sheet_parse_duration_before_fcp =
+        base::TimeDelta::FromSecondsD(
+            perf.authorStyleSheetParseDurationBeforeFCP());
+  }
   return timing;
 }
 
 std::unique_ptr<base::Timer> MetricsRenderFrameObserver::CreateTimer() const {
   return base::WrapUnique(new base::OneShotTimer);
 }
 
 bool MetricsRenderFrameObserver::HasNoRenderFrame() const {
   bool no_frame = !render_frame() || !render_frame()->GetWebFrame();
   DCHECK(!no_frame);
   return no_frame;
 }
 
 void MetricsRenderFrameObserver::OnDestruct() {
   delete this;
 }
 
 }  // namespace page_load_metrics