Fix scanning of escape codes.

src/lexer/experimental-scanner.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 544 matching lines @@
   switch (c) {
     case '\'':  // fall through
     case '"' :  // fall through
     case '\\': break;
     case 'b' : c = '\b'; break;
     case 'f' : c = '\f'; break;
     case 'n' : c = '\n'; break;
     case 'r' : c = '\r'; break;
     case 't' : c = '\t'; break;
     case 'u' : {
-      if (end > cursor + 4) return NULL;
+      ASSERT(cursor + 4 <= end);
       cursor = ScanHexNumber(cursor, cursor + 4, &c);
       if (cursor == NULL) return NULL;
       break;
     }
     case 'v' : c = '\v'; break;
     case 'x' : {
-      if (end > cursor + 2) return NULL ;
+      ASSERT(cursor + 2 <= end);
       cursor = ScanHexNumber(cursor, cursor + 2, &c);
       if (cursor == NULL) return NULL;
       break;
     }
     case '0' :  // fall through
     case '1' :  // fall through
     case '2' :  // fall through
     case '3' :  // fall through
     case '4' :  // fall through
     case '5' :  // fall through
     case '6' :  // fall through
     case '7' :
       if (end > cursor + 2) end = cursor + 2;
       cursor = ScanOctalEscape(cursor, end, &c); break;
   }
 
   // According to ECMA-262, section 7.8.4, characters not covered by the
   // above cases should be illegal, but they are commonly handled as
   // non-escaped characters by JS VMs.
   literal->AddChar(c);
   return cursor;
 }
 
 
 } }
 
 #endif  // V8_LEXER_EXPERIMENTAL_SCANNER_H