Add DocumentTiming metrics for "time to first text paint"

Source/platform/fonts/FontFallbackList.cpp

Index: Source/platform/fonts/FontFallbackList.cpp
diff --git a/Source/platform/fonts/FontFallbackList.cpp b/Source/platform/fonts/FontFallbackList.cpp
index d8eb999702eb9a4d9966a73bb086c4fe1a0bad31..b08441d13815cfedfded42bc0000d0dc5575ba34 100644
--- a/Source/platform/fonts/FontFallbackList.cpp
+++ b/Source/platform/fonts/FontFallbackList.cpp
@@ -46,6 +46,7 @@ FontFallbackList::FontFallbackList()
     , m_familyIndex(0)
     , m_generation(FontCache::fontCache()->generation())
     , m_hasLoadingFallback(false)
+    , m_hasCustomFont(false)
 {
 }
 
@@ -58,6 +59,7 @@ void FontFallbackList::invalidate(PassRefPtrWillBeRawPtr<FontSelector> fontSelec
     m_cachedPrimarySimpleFontData = 0;
     m_familyIndex = 0;
     m_hasLoadingFallback = false;
+    m_hasCustomFont = false;
     m_fontSelector = fontSelector;
     m_fontSelectorVersion = m_fontSelector ? m_fontSelector->version() : 0;
     m_generation = FontCache::fontCache()->generation();
@@ -90,14 +92,15 @@ bool FontFallbackList::loadingCustomFonts() const
 
 bool FontFallbackList::shouldSkipDrawing() const
 {
-    if (!m_hasLoadingFallback)
-        return false;
-
-    unsigned numFonts = m_fontList.size();
-    for (unsigned i = 0; i < numFonts; ++i) {
-        if (m_fontList[i]->shouldSkipDrawing())
-            return true;
+    if (m_hasLoadingFallback) {
+        unsigned numFonts = m_fontList.size();
+        for (unsigned i = 0; i < numFonts; ++i) {
+            if (m_fontList[i]->shouldSkipDrawing())
+                return true;
+        }
     }
+    if (m_fontSelector)
+        m_fontSelector->reportFirstNonBlankText(m_hasCustomFont);
     return false;
 }
 
@@ -210,6 +213,8 @@ const FontData* FontFallbackList::fontDataAt(const FontDescription& fontDescript
         m_fontList.append(result);
         if (result->isLoadingFallback())
             m_hasLoadingFallback = true;
+        if (result->isCustomFont())
+            m_hasCustomFont = true;
     }
     return result.get();
 }