dart2js cleanup: remove unused imports and variables

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

 // Copyright (c) 2012, 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.
 
 part of dart_backend;
 
 // TODO(ahe): This class is simply wrong.  This backend should use
 // elements when it can, not AST nodes.  Perhaps a [Map<Element,
 // TreeElements>] is what is needed.
 class ElementAst {
@@ skipping 299 matching lines @@
         ClassElement superclass = supertype.element;
         LibraryElement library = superclass.library;
         if (library.isPlatformLibrary) {
           if (_userImplementedPlatformClasses.add(superclass)) {
             // Register selectors for all instance methods since these might
             // be called on user classes from within the platform
             // implementation.
             superclass.forEachLocalMember((MemberElement element) {
               if (element.isConstructor || element.isStatic) return;
 
-              FunctionElement function = element.asFunctionElement();
               element.computeType(resolution);
               Selector selector = new Selector.fromElement(element);
               registerUse(new DynamicUse(selector, null));
             });
           }
         }
       }
     }
   }
 
@@ skipping 201 matching lines @@
   }
 
   // TODO(johnniwinther): Remove this when values are computed from the
   // expressions.
   @override
   void copyConstantValues(DartConstantTask task) {
     constantCompiler.constantValueMap
         .addAll(task.constantCompiler.constantValueMap);
   }
 }