Fix illegal escape-sequences to throw syntax errors.

src/scanner.h

Index: src/scanner.h
diff --git a/src/scanner.h b/src/scanner.h
index 045e7d27a6c647ee963a6c859c47b72548f1edf7..4de413b88538f52216ae8a907bdb8d7edb27f0ad 100644
--- a/src/scanner.h
+++ b/src/scanner.h
@@ -520,13 +520,16 @@ class Scanner {
   Token::Value ScanIdentifierOrKeyword();
   Token::Value ScanIdentifierSuffix(LiteralScope* literal);
 
-  void ScanEscape();
   Token::Value ScanString();
 
-  // Decodes a unicode escape-sequence which is part of an identifier.
+  // Scans an escape-sequence which is part of a string and adds the
+  // decoded character to the current literal. Returns true if a pattern
+  // is scanned.
+  bool ScanEscape();
+  // Decodes a Unicode escape-sequence which is part of an identifier.
   // If the escape sequence cannot be decoded the result is kBadChar.
   uc32 ScanIdentifierUnicodeEscape();
-  // Recognizes a uniocde escape-sequence and adds its characters,
+  // Scans a Unicode escape-sequence and adds its characters,
   // uninterpreted, to the current literal. Used for parsing RegExp
   // flags.
   bool ScanLiteralUnicodeEscape();