[regexp] parse RegExpUnicodeEscapeSequence according to spec.

src/regexp/regexp-parser.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_REGEXP_REGEXP_PARSER_H_
 #define V8_REGEXP_REGEXP_PARSER_H_
 
 #include "src/objects.h"
 #include "src/regexp/regexp-ast.h"
 #include "src/zone.h"
@@ skipping 84 matching lines @@
   T* last_;
 };
 
 
 // Accumulates RegExp atoms and assertions into lists of terms and alternatives.
 class RegExpBuilder : public ZoneObject {
  public:
   RegExpBuilder(Zone* zone, bool ignore_case, bool unicode);
   void AddCharacter(uc16 character);
   void AddUnicodeCharacter(uc32 character);
+  void AddEscapedUnicodeCharacter(uc32 character);
   // "Adds" an empty expression. Does nothing except consume a
   // following quantifier
   void AddEmpty();
   void AddCharacterClass(RegExpCharacterClass* cc);
   void AddCharacterClassForDesugaring(uc32 c);
   void AddAtom(RegExpTree* tree);
   void AddTerm(RegExpTree* tree);
   void AddAssertion(RegExpTree* tree);
   void NewAlternative();  // '|'
   bool AddQuantifierToAtom(int min, int max,
@@ skipping 174 matching lines @@
   bool simple_;
   bool contains_anchor_;
   bool is_scanned_for_captures_;
   bool failed_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_REGEXP_REGEXP_PARSER_H_