Use FontFallbackPriority Fonts in FontFallbackIterator

third_party/WebKit/Source/platform/fonts/FontFallbackIterator.cpp

Index: third_party/WebKit/Source/platform/fonts/FontFallbackIterator.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/FontFallbackIterator.cpp b/third_party/WebKit/Source/platform/fonts/FontFallbackIterator.cpp
index f13d587b3a6cf07ad0162214af6a87caf8922936..f425e26042a35a570da4d8d5875ff968d9facb2a 100644
--- a/third_party/WebKit/Source/platform/fonts/FontFallbackIterator.cpp
+++ b/third_party/WebKit/Source/platform/fonts/FontFallbackIterator.cpp
@@ -13,17 +13,38 @@
 
 namespace blink {
 
-PassRefPtr<FontFallbackIterator> FontFallbackIterator::create(const FontDescription& description, PassRefPtr<FontFallbackList> fallbackList)
+PassRefPtr<FontFallbackIterator> FontFallbackIterator::create(
+    const FontDescription& description,
+    PassRefPtr<FontFallbackList> fallbackList,
+    FontFallbackPriority fontFallbackPriority)
 {
-    return adoptRef(new FontFallbackIterator(description, fallbackList));
+    return adoptRef(new FontFallbackIterator(
+        description, fallbackList, fontFallbackPriority));
 }
 
-FontFallbackIterator::FontFallbackIterator(const FontDescription& description, PassRefPtr<FontFallbackList> fallbackList)
+FontFallbackIterator::FontFallbackIterator(const FontDescription& description,
+    PassRefPtr<FontFallbackList> fallbackList,
+    FontFallbackPriority fontFallbackPriority)
     : m_fontDescription(description)
     , m_fontFallbackList(fallbackList)
     , m_currentFontDataIndex(0)
     , m_segmentedIndex(0)
-    , m_fallbackStage(FontGroupFonts)
+    , m_fallbackStage(
+// Due to crbug.com/322658 we cannot reliably select Emoji fonts on Android at
+// the moment. Disabling this functionality on Android to avoid reports of
+// unreliable behavior until this issue is solved.
+#if !OS(ANDROID)
+    // Currently we have to push the Emoji font to the top of the list

[drott, 2016/02/05 13:29:18]

Looks like the windows failures indicate there is still some work required.
Overriding the font stack for symbols and math leads to unexpected results. So
it's better to address this issue first, then inserting the emoji and symbol
fonts before the system fonts in the fallback chain, but not before the CSS font
group fonts.

+    // due to https://github.com/behdad/harfbuzz/issues/217
+    isNonTextFallbackPriority(fontFallbackPriority)
+    ? FallbackPriorityFonts

[eae, 2016/02/17 18:55:17]

Indent line 40 and 41 one more level.

isNonTextFallbackPriority(fontFallbackPriority)
  ? FallbackPriorityFonts
  : FontGroupFonts

+    : FontGroupFonts
+#else
+    FontGroupFonts
+#endif
+    )
+    , m_fontFallbackPriority(fontFallbackPriority)
+    , m_symbolsFontCursor(0)
 {
 }
 
@@ -71,12 +92,17 @@ const FontDataRange FontFallbackIterator::next(const Vector<UChar32>& hintList)
     if (m_fallbackStage == OutOfLuck)
         return FontDataRange();
 
-    const FontData* fontData = m_fontFallbackList->fontDataAt(m_fontDescription, m_currentFontDataIndex);
+    if (m_fallbackStage == FallbackPriorityFonts) {
+        FontDataRange fallbackPriorityFont = nextFallbackPriorityFont();
+        if (!fallbackPriorityFont.isNull())
+            return fallbackPriorityFont;
+        // No more prioritized fallback fonts, proceed to processing the CSS
+        // defined fonts.
+        m_fallbackStage = FontGroupFonts;
+        return next(hintList);
+    }
 
-    // If there is no fontData coming from the fallback list, it means
-    // we have reached the system fallback stage.
-    if (!fontData) {
-        m_fallbackStage = SystemFonts;
+    if (m_fallbackStage == SystemFonts) {
         // We've reached pref + system fallback.
         ASSERT(hintList.size());
         RefPtr<SimpleFontData> systemFont = uniqueSystemFontForHint(hintList[0]);
@@ -95,6 +121,19 @@ const FontDataRange FontFallbackIterator::next(const Vector<UChar32>& hintList)
         return FontDataRange(lastResort);
     }
 
+    ASSERT(m_fallbackStage == FontGroupFonts
+        || m_fallbackStage == SegmentedFace);
+    const FontData* fontData = m_fontFallbackList->fontDataAt(
+        m_fontDescription, m_currentFontDataIndex);
+
+    if (!fontData) {
+        // If there is no fontData coming from the fallback list, it means
+        // we are now looking at system fonts, either for prioritized symbol
+        // or emoji fonts or by calling system fallback API.
+        m_fallbackStage = SystemFonts;
+        return next(hintList);
+    }
+
     // Otherwise we've received a fontData from the font-family: set of fonts,
     // and a non-segmented one in this case.
     if (!fontData->isSegmented()) {
@@ -137,6 +176,25 @@ const FontDataRange FontFallbackIterator::next(const Vector<UChar32>& hintList)
     return next(hintList);
 }
 
+FontDataRange FontFallbackIterator::nextFallbackPriorityFont()
+{
+    ASSERT(m_fontFallbackPriority != FontFallbackPriority::Invalid);
+    FontCache* fontCache = FontCache::fontCache();
+
+    const Vector<AtomicString>* priorityFontList =
+        fontCache->fontListForFallbackPriority(
+        m_fontDescription, m_fontFallbackPriority);
+
+    if (m_symbolsFontCursor == priorityFontList->size())
+        return FontDataRange();
+
+    RefPtr<SimpleFontData> priorityFont = fontCache->getFontData(
+        m_fontDescription,
+        priorityFontList->at(m_symbolsFontCursor));
+    m_symbolsFontCursor++;
+    return FontDataRange(priorityFont);
+}
+
 const PassRefPtr<SimpleFontData> FontFallbackIterator::uniqueSystemFontForHint(UChar32 hint)
 {
     FontCache* fontCache = FontCache::fontCache();