Add DocumentTiming metrics for "time to first text paint"

Source/core/timing/PerformanceTiming.cpp

Index: Source/core/timing/PerformanceTiming.cpp
diff --git a/Source/core/timing/PerformanceTiming.cpp b/Source/core/timing/PerformanceTiming.cpp
index ce7df6baaba9384ead75a57c31b5d2dfb1fb6026..61da2ddccad5b60ecfb81532d9a11392417d8cf2 100644
--- a/Source/core/timing/PerformanceTiming.cpp
+++ b/Source/core/timing/PerformanceTiming.cpp
@@ -322,6 +322,24 @@ unsigned long long PerformanceTiming::firstLayout() const
     return monotonicTimeToIntegerMilliseconds(timing->firstLayout());
 }
 
+unsigned long long PerformanceTiming::firstNonBlankText() const
+{
+    const DocumentTiming* timing = documentTiming();
+    if (!timing)
+        return 0;
+
+    return monotonicTimeToIntegerMilliseconds(timing->firstNonBlankText());
+}
+
+unsigned long long PerformanceTiming::firstCustomFontText() const
+{
+    const DocumentTiming* timing = documentTiming();
+    if (!timing)
+        return 0;
+
+    return monotonicTimeToIntegerMilliseconds(timing->firstCustomFontText());
+}
+
 DocumentLoader* PerformanceTiming::documentLoader() const
 {
     if (!m_frame)