Add some support for the code-point code-unit distinction.

runtime/vm/scanner.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // Scanner class for the Dart language. The scanner reads source text
 // and produces a stream of tokens which is used by the parser.
 //
 
 #ifndef VM_SCANNER_H_
 #define VM_SCANNER_H_
@@ skipping 28 matching lines @@
     int offset;               // Offset in source string.
     int length;               // Length of token in source.
     SourcePosition position;  // Text position in source.
     String* literal;          // Identifier, number or string literal.
   };
 
   // Dummy token index reflecting an unknown source position.
   static const intptr_t kDummyTokenIndex = 0;
 
   // Character used to indicate a private identifier.
-  static const char kPrivateIdentifierStart  = '_';
+  static const unsigned char kPrivateIdentifierStart  = '_';
 
   // Character used to separate the private identifier from the key.
   static const char kPrivateKeySeparator = '@';
 
   typedef ZoneGrowableArray<TokenDescriptor> GrowableTokenStream;
 
   // Initializes scanner to scan string source.
   Scanner(const String& source, const String& private_key);
   ~Scanner();
 
@@ skipping 156 matching lines @@
 
   SourcePosition c0_pos_;      // Source position of lookahead character c0_.
   KeywordTable keywords_[Token::numKeywords];
   Array& keyword_symbol_table_;  // Access to keyword symbols in object store.
 };
 
 
 }  // namespace dart
 
 #endif  // VM_SCANNER_H_