Allow the ZWJ and ZWNJ characters in IdentifierPart as per ES5.

src/char-predicates.h

Index: src/char-predicates.h
===================================================================
--- src/char-predicates.h	(revision 10785)
+++ src/char-predicates.h	(working copy)
@@ -56,6 +56,8 @@
 struct IdentifierPart {
   static inline bool Is(uc32 c) {
     return IdentifierStart::Is(c)
+        || c == 0x200C
+        || c == 0x200D

[mathias, 2012/02/22 09:49:37]

As an `IdentifierStart` character is the most common case for an
`IdentifierPart`, I figured it would be best to perform the U+200C and U+200D
checks right after, but before the more expensive Unicode category lookups.

[Lasse Reichstein Nielsen, 2012/02/22 14:03:28]

Good thought.
I'd prefer moving the number (digit, really) test before the ZWNJ/ZWJ test,
since digits are probably more likely to be in actual identifiers. 

Perhaps add a comment after the constants (like "  // U+200C is
ZeroWidthNonJoiner.").

         || unibrow::Number::Is(c)
         || unibrow::CombiningMark::Is(c)
         || unibrow::ConnectorPunctuation::Is(c);