Add DocumentTiming metrics for "time to first text paint"

Source/core/css/CSSFontSelector.cpp

Index: Source/core/css/CSSFontSelector.cpp
diff --git a/Source/core/css/CSSFontSelector.cpp b/Source/core/css/CSSFontSelector.cpp
index d984785f0638362ca88bdce4deb68553a3cea4a3..320a14dfb21c98ec0f50a5b2b2f75c9b0b10e988 100644
--- a/Source/core/css/CSSFontSelector.cpp
+++ b/Source/core/css/CSSFontSelector.cpp
@@ -148,6 +148,16 @@ void CSSFontSelector::willUseFontData(const FontDescription& fontDescription, co
         face->willUseFontData(fontDescription, character);
 }
 
+void CSSFontSelector::reportFirstCustomFontText()
+{
+    m_document->markFirstCustomFontText();
+}
+
+void CSSFontSelector::reportFirstNonBlankText()
+{
+    m_document->markFirstNonBlankText();
+}
+
 bool CSSFontSelector::isPlatformFontAvailable(const FontDescription& fontDescription, const AtomicString& passedFamily)
 {
     AtomicString family = familyNameFromSettings(m_genericFontFamilySettings, fontDescription, passedFamily);