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

third_party/WebKit/Source/core/timing/PerformanceTiming.h

Index: third_party/WebKit/Source/core/timing/PerformanceTiming.h
diff --git a/third_party/WebKit/Source/core/timing/PerformanceTiming.h b/third_party/WebKit/Source/core/timing/PerformanceTiming.h
index 8a84faf5dfe4e7069cfe6c99d9a19ead49ca5a93..1b2fed312992c0aca1c4234d4a689629defe12d9 100644
--- a/third_party/WebKit/Source/core/timing/PerformanceTiming.h
+++ b/third_party/WebKit/Source/core/timing/PerformanceTiming.h
@@ -38,6 +38,7 @@
 
 namespace blink {
 
+class CSSTiming;
 class DocumentLoadTiming;
 class DocumentLoader;
 class DocumentParserTiming;
@@ -107,6 +108,10 @@ class CORE_EXPORT PerformanceTiming final
   unsigned long long parseBlockedOnScriptExecutionFromDocumentWriteDuration()
       const;
 
+  // Microseconds spend parsing author style sheets before the first contentful
+  // paint.
+  unsigned long long authorStyleSheetParseDurationBeforeFCP() const;
+
   ScriptValue toJSONForBinding(ScriptState*) const;
 
   DECLARE_VIRTUAL_TRACE();
@@ -118,6 +123,7 @@ class CORE_EXPORT PerformanceTiming final
   explicit PerformanceTiming(LocalFrame*);
 
   const DocumentTiming* documentTiming() const;
+  const CSSTiming* cssTiming() const;
   const DocumentParserTiming* documentParserTiming() const;
   const PaintTiming* paintTiming() const;
   DocumentLoader* documentLoader() const;