Narrow String::CharAt from int32_t to uint16_t.

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_
 
 #include "vm/growable_array.h"
 #include "vm/token.h"
 
 namespace dart {
 
 // Forward declarations.
 class Array;
 class Library;
 class RawString;
 class ScanContext;
 class String;
 
 // A call to Scan() scans the source one token at at time.
 // The scanned token is returned by cur_token().
 // GetStream() scans the entire source text and returns a stream of tokens.
 class Scanner : ValueObject {
  public:
-  typedef int32_t (*CharAtFunc)(const String& str, intptr_t index);
+  typedef uint16_t (*CharAtFunc)(const String& str, intptr_t index);
 
   // SourcePosition describes a text location in user friendly
   // terms of line number and column.
   struct SourcePosition {
     int line;
     int column;
   };
 
   // TokenDesc defines the kind of a token and its location in
   // the source text.
@@ skipping 174 matching lines @@
   Isolate* isolate_;
 
   static KeywordTable keywords_[Token::kNumKeywords];
   static int keywords_char_offset_[kNumLowercaseChars];
 };
 
 
 }  // namespace dart
 
 #endif  // VM_SCANNER_H_