Add separate scanner only intended for preparsing.

src/scanner-base.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 23 matching lines @@
 #include "checks.h"
 #include "allocation.h"
 #include "token.h"
 #include "unicode-inl.h"
 #include "char-predicates.h"
 #include "utils.h"
 
 namespace v8 {
 namespace internal {
 
+// Interface through which the scanner reads characters from the input source.
+class UTF16Buffer {
+ public:
+  UTF16Buffer();
+  virtual ~UTF16Buffer() {}
+
+  virtual void PushBack(uc32 ch) = 0;
+  // Returns a value < 0 when the buffer end is reached.
+  virtual uc32 Advance() = 0;
+  virtual void SeekForward(int pos) = 0;
+
+  int pos() const { return pos_; }
+
+ protected:
+  int pos_;  // Current position in the buffer.
+  int end_;  // Position where scanning should stop (EOF).
+};
+
+
 class ScannerConstants : AllStatic {
  public:
   typedef unibrow::Utf8InputBuffer<1024> Utf8Decoder;
 
   static StaticResource<Utf8Decoder>* utf8_decoder() {
     return &utf8_decoder_;
   }
 
   static unibrow::Predicate<IdentifierStart, 128> kIsIdentifierStart;
   static unibrow::Predicate<IdentifierPart, 128> kIsIdentifierPart;
@@ skipping 124 matching lines @@
   // keyword with the current prefix).
   const char* keyword_;
   int counter_;
   Token::Value keyword_token_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SCANNER_BASE_H_