Add metrics for style update time before FCP.

chrome/common/page_load_metrics/page_load_timing.cc

Index: chrome/common/page_load_metrics/page_load_timing.cc
diff --git a/chrome/common/page_load_metrics/page_load_timing.cc b/chrome/common/page_load_metrics/page_load_timing.cc
index 40120a3a406d14b5696d9dfc4bed2026db9de77b..9ce7705baca0e990be0c45250ed031fdbc7374a6 100644
--- a/chrome/common/page_load_metrics/page_load_timing.cc
+++ b/chrome/common/page_load_metrics/page_load_timing.cc
@@ -14,11 +14,14 @@ StyleSheetTiming::~StyleSheetTiming() {}
 
 bool StyleSheetTiming::operator==(const StyleSheetTiming& other) const {
   return author_style_sheet_parse_duration_before_fcp ==
-         other.author_style_sheet_parse_duration_before_fcp;
+             other.author_style_sheet_parse_duration_before_fcp &&
+         update_style_duration_before_fcp ==
+             other.update_style_duration_before_fcp;
 }
 
 bool StyleSheetTiming::IsEmpty() const {
-  return !author_style_sheet_parse_duration_before_fcp;
+  return !author_style_sheet_parse_duration_before_fcp &&
+         !update_style_duration_before_fcp;
 }
 
 PageLoadTiming::PageLoadTiming() {}