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

pkg/compiler/lib/src/cps_ir/gvn.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.
 
 library dart2js.cps_ir.gvn;
 
 import 'cps_ir_nodes.dart';
-import '../universe/side_effects.dart';
 import '../elements/elements.dart';
 import 'optimizers.dart' show Pass;
 import 'loop_hierarchy.dart';
 import 'loop_effects.dart';
 import '../world.dart';
 import '../compiler.dart' show Compiler;
 import '../js_backend/js_backend.dart' show JavaScriptBackend;
-import '../constants/values.dart';
 import 'type_mask_system.dart';
 import 'effects.dart';
 
 /// Eliminates redundant primitives by reusing the value of another primitive
 /// that is known to have the same result.  Primitives are also hoisted out of
 /// loops when possible.
 ///
 /// Reusing values can introduce new temporaries, which in some cases is more
 /// expensive than recomputing the value on-demand. For example, pulling an
 /// expression such as "n+1" out of a loop is generally not worth it.
@@ skipping 582 matching lines @@
 
   @override
   processReference(Reference ref) {
     callback(ref);
   }
 
   static void forEach(Primitive node, ReferenceCallback callback) {
     new InputVisitor(callback).visit(node);
   }
 }