Fix analysis warnings.

lib/src/util/string_literal_iterator.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/ast.dart';
 
 // ASCII character codes.
 
@@ skipping 70 matching lines @@
   ///
   /// Throws an [ArgumentError] if [literal] contains interpolated strings.
   StringLiteralIterator(StringLiteral literal) {
     if (literal is StringInterpolation) {
       throw new ArgumentError("Can't iterate over an interpolated string.");
     } else if (literal is SimpleStringLiteral) {
       _strings.add(literal);
     } else {
       assert(literal is AdjacentStrings);
 
-      for (var string in literal.strings) {
+      for (var string in (literal as AdjacentStrings).strings) {
         if (string is StringInterpolation) {
           throw new ArgumentError("Can't iterate over an interpolated string.");
         }
         assert(string is SimpleStringLiteral);
         _strings.add(string);
       }
     }
 
     _offset = _strings.first.contentsOffset - 1;
   }
@@ skipping 134 matching lines @@
     return null;
   }
 
   /// Move [_runes] to the next rune and update [_nextOffset].
   bool _moveRunesNext() {
     var result = _runes.moveNext();
     _nextOffset++;
     return result;
   }
 }