Implement ES6 unicode escapes.

src/scanner.h

Index: src/scanner.h
diff --git a/src/scanner.h b/src/scanner.h
index e626f206c74952c856d77d55b708b9e01661b1ac..6d7180e0093f56457983cce9fba874aeff92226c 100644
--- a/src/scanner.h
+++ b/src/scanner.h
@@ -611,6 +611,10 @@ class Scanner {
   }
 
   uc32 ScanHexNumber(int expected_length);
+  // Scan a number of any length but not bigger than max_value. For example, the
+  // number can be 000000001, so it's very long in characters but its value is
+  // small.
+  uc32 ScanUnlimitedLengthHexNumber(int max_value);
 
   // Scans a single JavaScript token.
   void Scan();
@@ -637,6 +641,8 @@ class Scanner {
   // Decodes a Unicode escape-sequence which is part of an identifier.
   // If the escape sequence cannot be decoded the result is kBadChar.
   uc32 ScanIdentifierUnicodeEscape();
+  // Helper for the above functions.
+  uc32 ScanUnicodeEscape();
 
   // Return the current source position.
   int source_pos() {