Fix bug when the scanner does a pushback at the end of input.

src/scanner.h

 // Copyright 2010 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 25 matching lines @@
 namespace internal {
 
 // A buffered character stream based on a random access character
 // source (ReadBlock can be called with pos_ pointing to any position,
 // even positions before the current).
 class BufferedUC16CharacterStream: public UC16CharacterStream {
  public:
   BufferedUC16CharacterStream();
   virtual ~BufferedUC16CharacterStream();
 
-  virtual void PushBack(uc16 character);
+  virtual void PushBack(uc32 character);
 
  protected:
   static const unsigned kBufferSize = 512;
   static const unsigned kPushBackStepSize = 16;
 
   virtual unsigned SlowSeekForward(unsigned delta);
   virtual bool ReadBlock();
   virtual void SlowPushBack(uc16 character);
 
   virtual unsigned BufferSeekForward(unsigned delta) = 0;
@@ skipping 43 matching lines @@
 
 
 // UTF16 buffer to read characters from an external string.
 class ExternalTwoByteStringUC16CharacterStream: public UC16CharacterStream {
  public:
   ExternalTwoByteStringUC16CharacterStream(Handle<ExternalTwoByteString> data,
                                            int start_position,
                                            int end_position);
   virtual ~ExternalTwoByteStringUC16CharacterStream();
 
-  virtual void PushBack(uc16 character) {
+  virtual void PushBack(uc32 character) {
     ASSERT(buffer_cursor_ > raw_data_);
     buffer_cursor_--;
     pos_--;
   }
+
  protected:
   virtual unsigned SlowSeekForward(unsigned delta) {
     // Fast case always handles seeking.
     return 0;
   }
   virtual bool ReadBlock() {
     // Entire string is read at start.
     return false;
   }
   Handle<ExternalTwoByteString> source_;
@@ skipping 50 matching lines @@
 
   // Used to recognizes one of the literals "true", "false", or "null". These
   // are the only valid JSON identifiers (productions JSONBooleanLiteral,
   // JSONNullLiteral).
   Token::Value ScanJsonIdentifier(const char* text, Token::Value token);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_SCANNER_H_