Add DocumentTiming metrics for "time to first text paint"

Source/web/WebPerformance.cpp

Index: Source/web/WebPerformance.cpp
diff --git a/Source/web/WebPerformance.cpp b/Source/web/WebPerformance.cpp
index d48fc0c3ba61668567706586a52d86d995a44b19..47506ceaa13a8e9215b251289907036fc376f34c 100644
--- a/Source/web/WebPerformance.cpp
+++ b/Source/web/WebPerformance.cpp
@@ -171,6 +171,16 @@ double WebPerformance::firstLayout() const
     return millisecondsToSeconds(m_private->timing()->firstLayout());
 }
 
+double WebPerformance::firstNonBlankText() const
+{
+    return millisecondsToSeconds(m_private->timing()->firstNonBlankText());
+}
+
+double WebPerformance::firstCustomFontText() const
+{
+    return millisecondsToSeconds(m_private->timing()->firstCustomFontText());
+}
+
 WebPerformance::WebPerformance(const PassRefPtrWillBeRawPtr<Performance>& performance)
     : m_private(performance)
 {