pkg/compiler: clean up imports

pkg/compiler/lib/src/js_backend/checked_mode_helpers.dart

 // Copyright (c) 2013, 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 '../compiler.dart' show Compiler;
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../js/js.dart' as jsAst;
 import '../js/js.dart' show js;
 import '../ssa/codegen.dart' show SsaCodeGenerator;
-import '../ssa/nodes.dart' show HTypeConversion, HInstruction;
+import '../ssa/nodes.dart' show HTypeConversion;
 import '../universe/call_structure.dart' show CallStructure;
-import '../universe/use.dart'
-    show DynamicUse, StaticUse, StaticUseKind, TypeUse, TypeUseKind;
+import '../universe/use.dart' show StaticUse;
 import 'backend.dart';
 
 class CheckedModeHelper {
   final String name;
 
   const CheckedModeHelper(String this.name);
 
   StaticUse getStaticUse(Compiler compiler) {
     JavaScriptBackend backend = compiler.backend;
     return new StaticUse.staticInvoke(
@@ skipping 106 matching lines @@
     DartType type = node.typeExpression;
     Element element = type.element;
     jsAst.Name isField = codegen.backend.namer.operatorIs(element);
     arguments.add(js.quoteName(isField));
     codegen.use(node.typeRepresentation);
     arguments.add(codegen.pop());
     jsAst.Name asField = codegen.backend.namer.substitutionName(element);
     arguments.add(js.quoteName(asField));
   }
 }