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

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;
+};
+
 // 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();
 
   bool operator==(const PageLoadTiming& other) const;
@@ skipping 67 matching lines @@
 
   // Sum of times when the parser is executing a script that was inserted from
   // document.write. This duration must be less than or equal to
   // parse_blocked_on_script_load_duration. Note that this value may be updated
   // multiple times during the period between parse_start and parse_stop. Note
   // that some uncommon cases where scripts are loaded via document.write are
   // not currently covered by this field. See crbug/600711 for details.
   base::Optional<base::TimeDelta>
       parse_blocked_on_script_execution_from_document_write_duration;
 
+  StyleSheetTiming style_sheet_timing;
+
   // If you add additional members, also be sure to update operator==,
   // page_load_metrics_messages.h, and IsEmpty().
 };
 
 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_