dart2js cleanup: remove unused imports and variables

pkg/compiler/lib/src/cps_ir/cps_ir_builder.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.
 
 library dart2js.ir_builder;
 
 import '../closure.dart' as closure;
 import '../common.dart';
-import '../common/names.dart' show Names, Selectors;
+import '../common/names.dart' show Selectors;
 import '../compile_time_constants.dart' show BackendConstantEnvironment;
 import '../constants/constant_system.dart';
-import '../constants/values.dart' show ConstantValue, PrimitiveConstantValue;
+import '../constants/values.dart' show ConstantValue;
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../io/source_information.dart';
 import '../js/js.dart' as js
     show
         js,
         objectLiteral,
         Expression,
         LiteralStatement,
         Template,
         InterpolatedExpression,
         isIdentityTemplate;
 import '../native/native.dart' show NativeBehavior;
 import '../tree/tree.dart' as ast;
 import '../types/types.dart' show TypeMask;
 import '../universe/call_structure.dart' show CallStructure;
 import '../universe/selector.dart' show Selector, SelectorKind;
-
 import 'cps_ir_builder_task.dart' show GlobalProgramInformation;
 import 'cps_ir_nodes.dart' as ir;
 
 /// A mapping from variable elements to their compile-time values.
 ///
 /// Map elements denoted by parameters and local variables to the
 /// [ir.Primitive] that is their value.  Parameters and locals are
 /// assigned indexes which can be used to refer to them.
 class Environment {
   /// A map from locals to their environment index.
@@ skipping 2870 matching lines @@
       this.sourceInformation});
 }
 
 class SwitchCaseInfo {
   final SubbuildFunction buildCondition;
   final SubbuildFunction buildBody;
   final SourceInformation sourceInformation;
 
   SwitchCaseInfo(this.buildCondition, this.buildBody, this.sourceInformation);
 }