Visit 
https://ar-ar.facebook.com/campaign/landing.php?placement=pflo&campaign_id=402047449186&extra_1=auto with a debug build:

Activate a new font in Mac OS, trigger font cache invalidation.

Expected: No assertion failure.

Actual

ASSERTION FAILED: FontCache::fontCache()->generation() == m_generation
../../third_party/WebKit/Source/platform/fonts/FontFallbackList.cpp(222) : const blink::FontData *blink::FontFallbackList::fontDataAt(const blink::FontDescription &, unsigned int) const
1   0x11565353d blink::FontFallbackList::fontDataAt(blink::FontDescription const&, unsigned int) const
2   0x11564e3d8 blink::FontFallbackIterator::needsHintList() const
3   0x115691f76 blink::HarfBuzzShaper::shapeResult()
4   0x115684d25 blink::CachingWordShapeIterator::shapeWordWithoutSpacing(blink::TextRun const&, blink::Font const*)
5   0x1156845e2 blink::CachingWordShapeIterator::shapeWord(blink::TextRun const&, blink::Font const*)
6   0x115684819 blink::CachingWordShapeIterator::shapeToEndIndex(WTF::RefPtr<blink::ShapeResult const>*, unsigned int)
7   0x115684707 blink::CachingWordShapeIterator::nextWord(WTF::RefPtr<blink::ShapeResult const>*)
8   0x11568382e blink::CachingWordShapeIterator::next(WTF::RefPtr<blink::ShapeResult const>*)
9   0x11568359d blink::CachingWordShaper::width(blink::Font const*, blink::TextRun const&, WTF::HashSet<blink::SimpleFontData const*, WTF::PtrHash<blink::SimpleFontData const>, WTF::HashTraits<blink::SimpleFontData const*>, WTF::PartitionAllocator>*, blink::FloatRect*)
10  0x11561c3fe blink::Font::floatWidthForComplexText(blink::TextRun const&, WTF::HashSet<blink::SimpleFontData const*, WTF::PtrHash<blink::SimpleFontData const>, WTF::HashTraits<blink::SimpleFontData const*>, WTF::PartitionAllocator>*, blink::FloatRect*) const
11  0x11561c315 blink::Font::width(blink::TextRun const&, WTF::HashSet<blink::SimpleFontData const*, WTF::PtrHash<blink::SimpleFontData const>, WTF::HashTraits<blink::SimpleFontData const*>, WTF::PartitionAllocator>*, blink::FloatRect*) const
12  0x11768b30d blink::LayoutMenuList::computeTextHeight(blink::TextRun const&, blink::ComputedStyle const&) const