Reland of land "Change fallback font collection in HarfBuzzShaper"

Source/platform/fonts/shaping/HarfBuzzShaper.cpp

Index: Source/platform/fonts/shaping/HarfBuzzShaper.cpp
diff --git a/Source/platform/fonts/shaping/HarfBuzzShaper.cpp b/Source/platform/fonts/shaping/HarfBuzzShaper.cpp
index 32ba8965eb210519c970550b0b83fa2b0e7b5bfa..d9be39f6aab7699ec011ae7ce34786fc6253947d 100644
--- a/Source/platform/fonts/shaping/HarfBuzzShaper.cpp
+++ b/Source/platform/fonts/shaping/HarfBuzzShaper.cpp
@@ -481,6 +481,15 @@
     return charactersSoFar;
 }
 
+void ShapeResult::fallbackFonts(HashSet<const SimpleFontData*>* fallback) const
+{
+    ASSERT(fallback);
+    for (unsigned i = 0; i < m_runs.size(); ++i) {
+        if (m_runs[i] && m_runs[i]->m_fontData != m_primaryFont)
+            fallback->add(m_runs[i]->m_fontData);
+    }
+}
+
 unsigned ShapeResult::numberOfRunsForTesting() const
 {
     return m_runs.size();
@@ -567,17 +576,13 @@
     }
 }
 
-HarfBuzzShaper::HarfBuzzShaper(const Font* font, const TextRun& run,
-    HashSet<const SimpleFontData*>* fallbackFonts)
-    : Shaper(font, run, nullptr, fallbackFonts)
+HarfBuzzShaper::HarfBuzzShaper(const Font* font, const TextRun& run)
+    : Shaper(font, run)
     , m_normalizedBufferLength(0)
     , m_wordSpacingAdjustment(font->fontDescription().wordSpacing())
     , m_letterSpacing(font->fontDescription().letterSpacing())
     , m_expansionOpportunityCount(0)
 {
-    // TODO(eae): Once SimpleShaper is gone the ownership of this should shift
-    // to HarfBuzzShaper.
-    ASSERT(fallbackFonts);
     m_normalizedBuffer = adoptArrayPtr(new UChar[m_textRun.length() + 1]);
     normalizeCharacters(m_textRun, m_textRun.length(), m_normalizedBuffer.get(), &m_normalizedBufferLength);
     setExpansion(m_textRun.expansion());
@@ -939,8 +944,6 @@
 {
     ASSERT(endCharacter > startCharacter);
     ASSERT(script != USCRIPT_INVALID_CODE);
-    if (m_fallbackFonts)
-        trackNonPrimaryFallbackFont(fontData);
 
     hb_direction_t direction = TextDirectionToHBDirection(m_textRun.direction(),
         m_font->fontDescription().orientation(), fontData);
@@ -1102,7 +1105,6 @@
 
     run->m_width = totalAdvance > 0.0 ? totalAdvance : 0.0;
     result->m_width += run->m_width;
-    result->m_fallbackFonts = *m_fallbackFonts;
 }
 
 float HarfBuzzShaper::adjustSpacing(ShapeResult::RunInfo* run, size_t glyphIndex, unsigned currentCharacterIndex, float& offset, float& totalAdvance)