UMA histograms to measure whether / how long blank text is rendered for loading web fonts

Source/core/css/CSSCustomFontData.h

Index: Source/core/css/CSSCustomFontData.h
diff --git a/Source/core/css/CSSCustomFontData.h b/Source/core/css/CSSCustomFontData.h
index 206188854e91153a85ccb33d1c0d1a20c231583a..0a3d495e10cf556d80d6c69ba8335bedf5151700 100644
--- a/Source/core/css/CSSCustomFontData.h
+++ b/Source/core/css/CSSCustomFontData.h
@@ -35,6 +35,13 @@ public:
 
     virtual ~CSSCustomFontData() { }
 
+    virtual bool shouldSkipDrawing() const OVERRIDE
+    {
+        if (m_fontFaceSource)
+            m_fontFaceSource->paintRequested();
+        return m_fallbackVisibility == InvisibleFallback && m_isUsed;
+    }
+
     virtual void beginLoadIfNeeded() const OVERRIDE
     {
         if (!m_isUsed && m_isLoadingFallback && m_fontFaceSource) {