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

Source/core/css/CSSCustomFontData.h

 /*
  * Copyright (C) 2013 Google, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 17 matching lines @@
 
 class CSSCustomFontData FINAL : public CustomFontData {
 public:
     static PassRefPtr<CSSCustomFontData> create(bool isLoadingFallback = false, FallbackVisibility visibility = VisibleFallback)
     {
         return adoptRef(new CSSCustomFontData(isLoadingFallback, visibility));
     }
 
     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) {
             m_isUsed = true;
             m_fontFaceSource->beginLoadIfNeeded();
         }
     }
 
     virtual void setCSSFontFaceSource(CSSFontFaceSource* source) OVERRIDE { m_fontFaceSource = source; }
     virtual void clearCSSFontFaceSource() OVERRIDE { m_fontFaceSource = 0; }
 
 private:
     CSSCustomFontData(bool isLoadingFallback, FallbackVisibility visibility)
         : CustomFontData(isLoadingFallback, visibility)
         , m_fontFaceSource(0)
     {
     }
 
     CSSFontFaceSource* m_fontFaceSource;
 };
 
 }
 
 #endif // CSSCustomFontData_h