Add DocumentTiming metrics for "time to first text paint"

Source/core/dom/DocumentTiming.cpp

Index: Source/core/dom/DocumentTiming.cpp
diff --git a/Source/core/dom/DocumentTiming.cpp b/Source/core/dom/DocumentTiming.cpp
index 30887789e8ded8a4bb91306d517b75e6fc04122a..2c8979e6a00752de185fc31a0879a76f4272da15 100644
--- a/Source/core/dom/DocumentTiming.cpp
+++ b/Source/core/dom/DocumentTiming.cpp
@@ -19,6 +19,8 @@ DocumentTiming::DocumentTiming(Document& document)
     , m_domContentLoadedEventEnd(0.0)
     , m_domComplete(0.0)
     , m_firstLayout(0.0)
+    , m_firstNonBlankText(0.0)
+    , m_firstCustomFontText(0.0)
     , m_document(document)
 {
 }
@@ -76,4 +78,18 @@ void DocumentTiming::markFirstLayout()
     notifyDocumentTimingChanged();
 }
 
+void DocumentTiming::markFirstNonBlankText()
+{
+    m_firstNonBlankText = monotonicallyIncreasingTime();
+    TRACE_EVENT_MARK_WITH_TIMESTAMP("blink.user_timing", "firstNonBlankText", m_firstNonBlankText);
+    notifyDocumentTimingChanged();
+}
+
+void DocumentTiming::markFirstCustomFontText()
+{
+    m_firstCustomFontText = monotonicallyIncreasingTime();
+    TRACE_EVENT_MARK_WITH_TIMESTAMP("blink.user_timing", "firstCustomFontText", m_firstCustomFontText);
+    notifyDocumentTimingChanged();
+}
+
 } // namespace blink