Add DocumentTiming metrics for "time to first text paint"

Source/platform/fonts/FontFallbackList.cpp

Index: Source/platform/fonts/FontFallbackList.cpp
diff --git a/Source/platform/fonts/FontFallbackList.cpp b/Source/platform/fonts/FontFallbackList.cpp
index 284f6124f883c5305bc5d99b66b7b8ddc7310688..b38c11b59c5a6c4a81565bac32abf1a0d85d3259 100644
--- a/Source/platform/fonts/FontFallbackList.cpp
+++ b/Source/platform/fonts/FontFallbackList.cpp
@@ -46,6 +46,7 @@ FontFallbackList::FontFallbackList()
     , m_familyIndex(0)
     , m_generation(FontCache::fontCache()->generation())
     , m_hasLoadingFallback(false)
+    , m_hasCustomFont(false)
 {
 }
 
@@ -58,6 +59,7 @@ void FontFallbackList::invalidate(PassRefPtrWillBeRawPtr<FontSelector> fontSelec
     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;
@@ -91,14 +93,15 @@ bool FontFallbackList::loadingCustomFonts() const
 
 bool FontFallbackList::shouldSkipDrawing() const
 {
-    if (!m_hasLoadingFallback)
-        return false;
-
-    unsigned numFonts = m_fontList.size();
-    for (unsigned i = 0; i < numFonts; ++i) {
-        if (m_fontList[i]->shouldSkipDrawing())
-            return true;
+    if (m_hasLoadingFallback) {
+        unsigned numFonts = m_fontList.size();
+        for (unsigned i = 0; i < numFonts; ++i) {
+            if (m_fontList[i]->shouldSkipDrawing())
+                return true;
+        }
     }
+    if (m_fontSelector)
+        m_fontSelector->reportFirstNonBlankText(m_hasCustomFont);

[Bryan McQuade, 2015/09/15 17:24:17]

I'm still learning this code so I may be misunderstanding, but given that
shouldSkipDrawing is a const method, which from its method signature appears to
not have side effects, I worry a little bit about depending on when/where such a
method gets called to record the first non-blank text. Would it make sense to
move this to the code that is actually responsible for drawing text, perhaps
somewhere in the Font class?

[Kunihiko Sakamoto, 2015/09/16 05:37:03]

Agreed that reporting from shouldXXX is confusing. Moved this to the caller side
(Font::drawText is also a const method, but it having side effects may be less
counter-intuitive).

     return false;
 }
 
@@ -211,6 +214,8 @@ const FontData* FontFallbackList::fontDataAt(const FontDescription& fontDescript
         m_fontList.append(result);
         if (result->isLoadingFallback())
             m_hasLoadingFallback = true;
+        if (result->isCustomFont())
+            m_hasCustomFont = true;
     }
     return result.get();
 }