Change code to remove two warnings that are reported when running build.py.

pkg/compiler/lib/src/resolution/send_structure.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.
 
 library dart2js.send_structure;
 
 import 'access_semantics.dart';
 import 'operators.dart';
 import 'semantic_visitor.dart';
 import '../dart_types.dart';
@@ skipping 693 matching lines @@
         // TODO(johnniwinther): Should this be a valid case?
         break;
       case AccessKind.UNRESOLVED_SUPER:
         // TODO(johnniwinther): Handle this separately.
       case AccessKind.UNRESOLVED:
         return visitor.errorUnresolvedSet(
             node,
             semantics.element,
             node.arguments.single,
             arg);
-        break;
       case AccessKind.COMPOUND:
         // This is not a valid case.
         break;
     }
     throw new SpannableAssertionFailure(node, "Invalid setter: ${semantics}");
   }
 
   String toString() => 'set($selector,$semantics)';
 }
 
@@ skipping 1438 matching lines @@
   final ConstructorElement constructor;
   final Selector selector;
 
   ThisConstructorInvokeStructure(this.constructor, this.selector);
 
   R dispatch(SemanticDeclarationVisitor<R, A> visitor, Send node, A arg) {
     return visitor.visitThisConstructorInvoke(
         node, constructor, node.argumentsNode, selector, arg);
   }
 }