Implement ES6 unicode escapes.

src/parser.h

Index: src/parser.h
diff --git a/src/parser.h b/src/parser.h
index c815a4546257ef74b0ae3bb2b94778b3c0abc648..dccd0a49689d5c374e416d7a34f77aca60ace68e 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -240,6 +240,10 @@ class RegExpParser BASE_EMBEDDED {
   // Checks whether the following is a length-digit hexadecimal number,
   // and sets the value if it is.
   bool ParseHexEscape(int length, uc32* value);
+  // Like ParseHexEscape, but the length of the number is unlimited; the value
+  // must be at most max_value.
+  bool ParseUnlimitedLengthHexEscape(int max_value, uc32* value);
+  bool ParseUnicodeEscape(uc32* value);
 
   uc32 ParseOctalLiteral();