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

Source/core/dom/FirstLetterPseudoElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. 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
@@ skipping 12 matching lines @@
 
 #include "config.h"
 #include "core/dom/FirstLetterPseudoElement.h"
 
 #include "core/dom/Element.h"
 #include "core/layout/GeneratedChildren.h"
 #include "core/layout/LayoutObject.h"
 #include "core/layout/LayoutObjectInlines.h"
 #include "core/layout/LayoutText.h"
 #include "core/layout/LayoutTextFragment.h"
+#include "platform/text/TextBreakIterator.h"
 #include "wtf/TemporaryChange.h"
 #include "wtf/text/WTFString.h"
 #include "wtf/text/icu/UnicodeIcu.h"
 
 namespace blink {
 
 using namespace WTF;
 using namespace Unicode;
 
 // CSS 2.1 http://www.w3.org/TR/CSS21/selector.html#first-letter
@@ skipping 27 matching lines @@
         length++;
     // Now account for leading punctuation.
     while (length < textLength && isPunctuationForFirstLetter(text[length]))
         length++;
 
     // Bail if we didn't find a letter before the end of the text or before a space.
     if (isSpaceForFirstLetter(text[length]) || length == textLength)
         return 0;
 
     // Account the next character for first letter.
-    length++;
+    const String substring = text.is8Bit() ? String::make16BitFrom8BitSource(text.substring(length).characters8(), textLength - length) : text.substring(length);
+    length += countCharactersAndGraphemesInCluster(substring.characters16(), substring.length(), 0, 1).characters;
 
     // Keep looking for allowed punctuation for the :first-letter.
     for (; length < textLength; ++length) {
         UChar c = text[length];
         if (!isPunctuationForFirstLetter(c))
             break;
     }
     return length;
 }
 
@@ skipping 220 matching lines @@
 
         // We only manage the style for the generated content items.
         if (!child->isText() && !child->isQuote() && !child->isImage())
             continue;
 
         child->setPseudoStyle(layoutObject->mutableStyle());
     }
 }
 
 } // namespace blink