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

third_party/WebKit/Source/core/css/CSSTiming.h

Index: third_party/WebKit/Source/core/css/CSSTiming.h
diff --git a/third_party/WebKit/Source/core/css/CSSTiming.h b/third_party/WebKit/Source/core/css/CSSTiming.h
new file mode 100644
index 0000000000000000000000000000000000000000..3e9873e4f3e31fa10a8067ef878a1df0efdd4a20
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+++ b/third_party/WebKit/Source/core/css/CSSTiming.h
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+// Copyright 2016 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 CSSTiming_h
+#define CSSTiming_h
+
+#include "core/dom/Document.h"
+#include "platform/Supplementable.h"
+#include "platform/heap/Handle.h"
+#include "wtf/Noncopyable.h"
+
+namespace blink {
+
+class PaintTiming;
+
+class CSSTiming : public GarbageCollectedFinalized<CSSTiming>,
+                  public Supplement<Document> {
+  WTF_MAKE_NONCOPYABLE(CSSTiming);
+  USING_GARBAGE_COLLECTED_MIXIN(CSSTiming);
+
+ public:
+  virtual ~CSSTiming() {}
+
+  // TODO(csharrison): Also record update style time before first paint.
+  void recordAuthorStyleSheetParseTime(double seconds);
+
+  double authorStyleSheetParseDurationBeforeFCP() const {
+    return m_parseTimeBeforeFCP;
+  }
+
+  static CSSTiming& from(Document&);
+  DECLARE_VIRTUAL_TRACE();
+
+ private:
+  explicit CSSTiming(Document&);
+
+  double m_parseTimeBeforeFCP = 0;
+
+  Member<Document> m_document;
+  Member<PaintTiming> m_paintTiming;
+};
+
+}  // namespace blink
+
+#endif  // CSSTiming_h