Cleanup 1: split parts into their own libraries, remove unused imports

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.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_nodes;
 
 import 'dart:collection';
 import 'cps_fragment.dart' show CpsFragment;
 import 'cps_ir_nodes_sexpr.dart';
 import '../constants/values.dart' as values;
 import '../dart_types.dart' show DartType, InterfaceType, TypeVariableType;
 import '../elements/elements.dart';
 import '../io/source_information.dart' show SourceInformation;
 import '../types/types.dart' show TypeMask;
 import '../universe/selector.dart' show Selector;
-import '../universe/side_effects.dart';
 
 import 'builtin_operator.dart';
 export 'builtin_operator.dart';
 
 import 'effects.dart';
 
 // These imports are only used for the JavaScript specific nodes.  If we want to
 // support more than one native backend, we should probably create better
 // abstractions for native code and its type and effect system.
 import '../js/js.dart' as js show Template, isNullGuardOnFirstArgument;
@@ skipping 3058 matching lines @@
     plug(new Branch.loose(
         _definitions.getCopy(node.conditionRef),
         _copies[node.trueContinuation],
         _copies[node.falseContinuation])..isStrictCheck = node.isStrictCheck);
   }
 
   visitUnreachable(Unreachable node) {
     plug(new Unreachable());
   }
 }