Do not break after ZWJ if the trailing character is Emoji.

third_party/WebKit/Source/platform/text/Character.h

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 94 matching lines @@
             || c == objectReplacementCharacter;
     }
     static bool canReceiveTextEmphasis(UChar32);
 
     static bool isGraphemeExtended(UChar32 c)
     {
         // http://unicode.org/reports/tr29/#Extend
         return u_hasBinaryProperty(c, UCHAR_GRAPHEME_EXTEND);
     }
 
+    static bool isEmoji(UChar32);

[tkent, 2016/04/20 01:56:28]

Need a comment.  Difference between isEmoji and following functions looks
unclear to me.

[Seigo Nonaka, 2016/04/20 07:39:41]

Done.

     // Default presentation style according to:
     // http://www.unicode.org/reports/tr51/#Presentation_Style
     static bool isEmojiTextDefault(UChar32);
     static bool isEmojiEmojiDefault(UChar32);
     static bool isEmojiModifierBase(UChar32);
     static bool isEmojiKeycapBase(UChar32);
     static bool isRegionalIndicator(UChar32);
     static bool isModifier(UChar32 c)
     {
         return c >= 0x1F3FB && c <= 0x1F3FF;
@@ skipping 24 matching lines @@
 
     static String normalizeSpaces(const LChar*, unsigned length);
     static String normalizeSpaces(const UChar*, unsigned length);
 
     static bool isCommonOrInheritedScript(UChar32);
 };
 
 } // namespace blink
 
 #endif