Add DocumentTiming metrics for "time to first text paint"

Source/platform/fonts/FontFallbackList.cpp

 /*
  * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 28 matching lines @@
 namespace blink {
 
 FontFallbackList::FontFallbackList()
     : m_pageZero(0)
     , m_cachedPrimarySimpleFontData(0)
     , m_fontSelector(nullptr)
     , m_fontSelectorVersion(0)
     , m_familyIndex(0)
     , m_generation(FontCache::fontCache()->generation())
     , m_hasLoadingFallback(false)
+    , m_hasCustomFont(false)
 {
 }
 
 void FontFallbackList::invalidate(PassRefPtrWillBeRawPtr<FontSelector> fontSelector)
 {
     releaseFontData();
     m_fontList.clear();
     m_pageZero = 0;
     m_pages.clear();
     m_cachedPrimarySimpleFontData = 0;
     m_familyIndex = 0;
     m_hasLoadingFallback = false;
+    m_hasCustomFont = false;
     if (m_fontSelector != fontSelector)
         m_fontSelector = fontSelector;
     m_fontSelectorVersion = m_fontSelector ? m_fontSelector->version() : 0;
     m_generation = FontCache::fontCache()->generation();
     m_cachingWordShaper.clear();
 }
 
 void FontFallbackList::releaseFontData()
 {
     unsigned numFonts = m_fontList.size();
@@ skipping 133 matching lines @@
     // Ask the font cache for the font data.
     // We are obtaining this font for the first time.  We keep track of the families we've looked at before
     // in |m_familyIndex|, so that we never scan the same spot in the list twice.  getFontData will adjust our
     // |m_familyIndex| as it scans for the right font to make.
     ASSERT(FontCache::fontCache()->generation() == m_generation);
     RefPtr<FontData> result = getFontData(fontDescription, m_familyIndex);
     if (result) {
         m_fontList.append(result);
         if (result->isLoadingFallback())
             m_hasLoadingFallback = true;
+        if (result->isCustomFont())

[drott, 2015/09/16 07:26:20]

Note that recording the m_hasCustomFont flag here, when fontDataAt(a) is called
with an index that points to a custom font, is not 100% equivalent to the
accessed font getting used for drawing. This might make the intended UMA data
you're trying to record inaccurate.

Instead, you might want to check whether SimpleFontData->isCustomFont() in
drawGlyphBuffer() - however, as I mentioned before, somehow it needs to be
ensure that we do this really only once per pageload and avoid introducing
additional cycles into drawGlyphBuffer.

[Kunihiko Sakamoto, 2015/09/17 08:36:10]

I see your point, but I think this condition is appropriate for our purpose.

Rather than actual font used for drawing, I'm interested in distinguishing if
the text paint is blocked by font load or not. If a webfont is loaded and then
fallbacked to local font (e.g. because loaded font did not have a glyph), we'd
like to count it as "custom font text".

+            m_hasCustomFont = true;
     }
     return result.get();
 }
 
 bool FontFallbackList::isValid() const
 {
     if (!m_fontSelector)
         return m_fontSelectorVersion == 0;
 
     return m_fontSelector->version() == m_fontSelectorVersion;
 }
 
 } // namespace blink