Add DocumentTiming metrics for "time to first text paint"

Source/core/css/CSSFontSelector.h

 /*
  * Copyright (C) 2007, 2008, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 32 matching lines @@
 class FontDescription;
 
 class CORE_EXPORT CSSFontSelector : public FontSelector {
 public:
     static PassRefPtrWillBeRawPtr<CSSFontSelector> create(Document* document)
     {
         return adoptRefWillBeNoop(new CSSFontSelector(document));
     }
     ~CSSFontSelector() override;
 
+    // FontSelector implementation
     unsigned version() const override { return m_fontFaceCache.version(); }
-
     PassRefPtr<FontData> getFontData(const FontDescription&, const AtomicString&) override;
     void willUseFontData(const FontDescription&, const AtomicString& family, UChar32) override;
+    void reportFirstCustomFontText() override;
+    void reportFirstNonBlankText() override;
+
     bool isPlatformFontAvailable(const FontDescription&, const AtomicString& family);
 
 #if !ENABLE(OILPAN)
     void clearDocument();
 #endif
 
     void fontFaceInvalidated();
 
     // FontCacheClient implementation
     void fontCacheInvalidated() override;
@@ skipping 26 matching lines @@
     FontFaceCache m_fontFaceCache;
     WillBeHeapHashSet<RawPtrWillBeWeakMember<CSSFontSelectorClient>> m_clients;
 
     RefPtrWillBeMember<FontLoader> m_fontLoader;
     GenericFontFamilySettings m_genericFontFamilySettings;
 };
 
 } // namespace blink
 
 #endif // CSSFontSelector_h