Fix 56 hints in pkg/compiler

pkg/compiler/lib/src/js_emitter/native_emitter.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 dart2js.js_emitter;
 
 class NativeEmitter {
 
   final Map<Element, ClassBuilder> cachedBuilders;
 
@@ skipping 296 matching lines @@
       int indexOfLastOptionalArgumentInParameters) {
     // The target JS function may check arguments.length so we need to
     // make sure not to pass any unspecified optional arguments to it.
     // For example, for the following Dart method:
     //   foo([x, y, z]);
     // The call:
     //   foo(y: 1)
     // must be turned into a JS call to:
     //   foo(null, y).
 
-    ClassElement classElement = member.enclosingClass;
-
     List<jsAst.Statement> statements = <jsAst.Statement>[];
     potentiallyConvertDartClosuresToJs(statements, member, stubParameters);
 
     String target;
     jsAst.Expression receiver;
     List<jsAst.Expression> arguments;
 
     assert(invariant(member, nativeMethods.contains(member)));
     // When calling a JS method, we call it with the native name, and only the
     // arguments up until the last one provided.
@@ skipping 137 matching lines @@
           }
     ''', {'info': infoAccess,
           'constructor': constructorAccess,
           'subclassRead': subclassRead,
           'interceptorsByTagAccess': interceptorsByTagAccess,
           'leafTagsAccess': leafTagsAccess,
           'nativeSuperclassTagName': embeddedNames.NATIVE_SUPERCLASS_TAG_NAME,
           'allowNativesSubclassing': true});
   }
 }