Add DocumentTiming metrics for "time to first text paint"

Source/platform/fonts/FontSelector.h

Index: Source/platform/fonts/FontSelector.h
diff --git a/Source/platform/fonts/FontSelector.h b/Source/platform/fonts/FontSelector.h
index 8bd8c8686de4f045eb9d031abd477d5483aa98a5..fbe8eca2b0e128b89b15ccdc8136c1c15fa201a7 100644
--- a/Source/platform/fonts/FontSelector.h
+++ b/Source/platform/fonts/FontSelector.h
@@ -42,6 +42,7 @@ public:
     virtual ~FontSelector() { }
     virtual PassRefPtr<FontData> getFontData(const FontDescription&, const AtomicString& familyName) = 0;
     virtual void willUseFontData(const FontDescription&, const AtomicString& familyName, UChar32) = 0;
+    virtual void reportFirstNonBlankText(bool isCustomFont) { }

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

I would prefer to have both reportFirstNonBlankText &
reportFirstCustomFontText() here instead of a magic boolean. That said - could
you think of a better way to get the timestamps recorded in UMA other than using
FontSelector as a bridge to access the document? The method does not fit so well
into the purpose of FontSelector.

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

Changed it to two methods.

Unfortunately, relation between Font class and Document is pretty weak so I
couldn't come up with a better way to route this. We might be able to make this
look less weird, by introducing a new interface. For example:

class TextTiming {
  virtual void reportFirstCustomFontText();
  virtual void reportFirstNonBlankText();
};

class FontSelector {
  TextTiming* textTiming();
};

What do you think?

 
     virtual unsigned version() const = 0;
 };