Fix 56 hints in pkg/compiler

pkg/compiler/lib/src/dart_backend/backend_ast_nodes.dart

 // Copyright (c) 2014, 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.
 
 library backend_ast_nodes;
 
 import '../constants/values.dart' as values;
 import '../dart_types.dart' as types;
 import '../elements/elements.dart' as elements;
 import '../tree/tree.dart' as tree;
@@ skipping 1029 matching lines @@
       });
     } else if (e is This) {
       write('this');
     } else {
       throw "Unexpected expression: $e";
     }
   }
 
   void writeParameters(Parameters params) {
     write('(');
-    bool first = true;
     writeEach(',', params.requiredParameters, (Parameter p) {
       if (p.type != null) {
         writeType(p.type);
         write(' ');
       }
       write(p.name);
       if (p.parameters != null) {
         writeParameters(p.parameters);
       }
     });
@@ skipping 508 matching lines @@
 class OpenStringChunk {
   final StringChunk previous;
   final tree.StringQuoting quoting;
   num cost;
 
   OpenStringChunk(this.previous, this.quoting, this.cost);
 
   StringChunk end(int endIndex) {
     return new StringChunk(previous, quoting, endIndex);
   }
-}
+}