Add metrics for style update time before FCP.

chrome/common/page_load_metrics/page_load_timing.h

 // 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.
 
 #ifndef CHROME_COMMON_PAGE_LOAD_METRICS_PAGE_LOAD_TIMING_H_
 #define CHROME_COMMON_PAGE_LOAD_METRICS_PAGE_LOAD_TIMING_H_
 
 #include "base/optional.h"
 #include "base/time/time.h"
 #include "third_party/WebKit/public/platform/WebLoadingBehaviorFlag.h"
 
 namespace page_load_metrics {
 
 struct StyleSheetTiming {
   StyleSheetTiming();
   StyleSheetTiming(const StyleSheetTiming& other);
   ~StyleSheetTiming();
 
   bool operator==(const StyleSheetTiming& other) const;
   bool operator!=(const StyleSheetTiming& other) const {
     return !(*this == other);
   }
 
   bool IsEmpty() const;
 
   // Total time spent parsing author style sheets, before the first contentful
   // paint.
   base::Optional<base::TimeDelta> author_style_sheet_parse_duration_before_fcp;
+
+  // Time spent in Document::updateStyle before FCP.
+  base::Optional<base::TimeDelta> update_style_duration_before_fcp;
 };
 
 // PageLoadTiming contains timing metrics associated with a page load. Many of
 // the metrics here are based on the Navigation Timing spec:
 // http://www.w3.org/TR/navigation-timing/.
 struct PageLoadTiming {
  public:
   PageLoadTiming();
   PageLoadTiming(const PageLoadTiming& other);
   ~PageLoadTiming();
@@ skipping 85 matching lines @@
 struct PageLoadMetadata {
   PageLoadMetadata();
   bool operator==(const PageLoadMetadata& other) const;
   // These are packed blink::WebLoadingBehaviorFlag enums.
   int behavior_flags = blink::WebLoadingBehaviorNone;
 };
 
 }  // namespace page_load_metrics
 
 #endif  // CHROME_COMMON_PAGE_LOAD_METRICS_PAGE_LOAD_TIMING_H_