Elements whose contents start with an astral Unicode symbol disappear when CSS `::first-letter` is …

Source/platform/text/TextBreakIterator.h

 /*
  * Copyright (C) 2006 Lars Knoll <lars@trolltech.com>
  * Copyright (C) 2007, 2011, 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 12 matching lines @@
 #define TextBreakIterator_h
 
 #include "platform/PlatformExport.h"
 #include "wtf/text/AtomicString.h"
 #include "wtf/text/Unicode.h"
 
 #include <unicode/brkiter.h>
 
 namespace blink {
 
+struct ClusterData {
+    ClusterData(unsigned numGraphemes, unsigned numCharacters)
+        : graphemes(numGraphemes)
+        , characters(numCharacters)
+    { }
+    unsigned graphemes;
+    unsigned characters;
+};
+
 typedef icu::BreakIterator TextBreakIterator;
 
 // Note: The returned iterator is good only until you get another iterator, with the exception of acquireLineBreakIterator.
 
 // This is similar to character break iterator in most cases, but is subject to
 // platform UI conventions. One notable example where this can be different
 // from character break iterator is Thai prepend characters, see bug 24342.
 // Use this for insertion point and selection manipulations.
 PLATFORM_EXPORT TextBreakIterator* cursorMovementIterator(const UChar*, int length);
 
@@ skipping 205 matching lines @@
     unsigned m_length;
 
     // For 16 bit strings, we use a TextBreakIterator.
     TextBreakIterator* m_iterator;
 };
 
 // Counts the number of grapheme clusters. A surrogate pair or a sequence
 // of a non-combining character and following combining characters is
 // counted as 1 grapheme cluster.
 PLATFORM_EXPORT unsigned numGraphemeClusters(const String&);
+// Counts the number of graphemes and characters.
+PLATFORM_EXPORT ClusterData countCharactersAndGraphemesInCluster(const UChar* normalizedBuffer, unsigned normalizedBufferLength, uint16_t startIndex, uint16_t endIndex);
 
 }
 
 #endif