dart2js cleanup: remove unused imports and variables

pkg/compiler/lib/src/js_backend/lookup_map_analysis.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.
 
 /// Analysis to determine how to generate code for `LookupMap`s.
 library compiler.src.js_backend.lookup_map_analysis;
 
+import 'package:pub_semver/pub_semver.dart';
+
 import '../common.dart';
 import '../common/registry.dart' show Registry;
 import '../compiler.dart' show Compiler;
 import '../constants/values.dart'
     show
         ConstantValue,
         ConstructedConstantValue,
         ListConstantValue,
         NullConstantValue,
         StringConstantValue,
         TypeConstantValue;
 import '../dart_types.dart' show DartType;
+import '../dart_types.dart' show InterfaceType;
 import '../elements/elements.dart'
-    show
-        ClassElement,
-        Element,
-        Elements,
-        FieldElement,
-        FunctionElement,
-        FunctionSignature,
-        LibraryElement,
-        VariableElement;
+    show ClassElement, FieldElement, LibraryElement, VariableElement;
 import 'js_backend.dart' show JavaScriptBackend;
-import '../dart_types.dart' show DynamicType, InterfaceType;
-import 'package:pub_semver/pub_semver.dart';
 
 /// An analysis and optimization to remove unused entries from a `LookupMap`.
 ///
 /// `LookupMaps` are defined in `package:lookup_map/lookup_map.dart`. They are
 /// simple maps that contain constant expressions as keys, and that only support
 /// the lookup operation.
 ///
 /// This analysis and optimization will tree-shake the contents of the maps by
 /// looking at the program and finding which keys are clearly unused. Not all
 /// constants can be approximated statically, so this optimization is limited to
@@ skipping 393 matching lines @@
         original.fields[analysis.valueField] = keyValuePairs[1];
       }
     } else {
       original.fields[analysis.entriesField] =
           new ListConstantValue(listType, keyValuePairs);
     }
   }
 }
 
 final _validLookupMapVersionConstraint = new VersionConstraint.parse('^0.0.1');