Add DocumentTiming metrics for "time to first text paint"

Source/platform/fonts/Font.cpp

Index: Source/platform/fonts/Font.cpp
diff --git a/Source/platform/fonts/Font.cpp b/Source/platform/fonts/Font.cpp
index aa087069dcd1202865b9e157dacb175a2be0e576..0a3eecbbe6b5efcfe22ec73c76549e01a59f361c 100644
--- a/Source/platform/fonts/Font.cpp
+++ b/Source/platform/fonts/Font.cpp
@@ -143,6 +143,9 @@ void Font::drawText(SkCanvas* canvas, const TextRunPaintInfo& runInfo,
     if (shouldSkipDrawing())
         return;
 
+    if (fontSelector())

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

If I am not mistaken, this keeps calling reportFirstNonBlankText reporting, and
calling up to m_document of CSSFontSelector for every draw call. The
Font::drawText is a highly performance sensitive function - I would prefer not
to introduce additional callback hooks into it.

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

That's right - I optimistically assumed the function call cost would be small
compared to actual font drawing.
Added a flag so that calling up to Document occurs at most once per Font
instance.

+        fontSelector()->reportFirstNonBlankText(m_fontFallbackList->hasCustomFont());
+
     if (runInfo.cachedTextBlob && runInfo.cachedTextBlob->get()) {
         // we have a pre-cached blob -- happy joy!
         drawTextBlob(canvas, paint, runInfo.cachedTextBlob->get(), point.data());
@@ -163,6 +166,9 @@ void Font::drawBidiText(SkCanvas* canvas, const TextRunPaintInfo& runInfo, const
     if (shouldSkipDrawing() && customFontNotReadyAction == DoNotPaintIfFontNotReady)
         return;
 
+    if (fontSelector())

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

Dito.

+        fontSelector()->reportFirstNonBlankText(m_fontFallbackList->hasCustomFont());
+
     // sub-run painting is not supported for Bidi text.
     const TextRun& run = runInfo.run;
     ASSERT((runInfo.from == 0) && (runInfo.to == run.length()));