dart2js cleanup: remove unused imports and variables

pkg/compiler/lib/src/ssa/value_range_analyzer.dart

 // Copyright (c) 2012, 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 '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
+import '../common/codegen.dart' show CodegenWorkItem;
 import '../compiler.dart' show Compiler;
 import '../constant_system_dart.dart';
 import '../constants/constant_system.dart';
 import '../constants/values.dart';
 import '../js_backend/js_backend.dart';
-
 import 'nodes.dart';
 import 'optimize.dart';
 
 class ValueRangeInfo {
   final ConstantSystem constantSystem;
 
   IntValue intZero;
   IntValue intOne;
 
   ValueRangeInfo(this.constantSystem) {
@@ skipping 1061 matching lines @@
   }
 
   Range handleBinaryOperation(HBinaryArithmetic instruction) {
     Range leftRange = visit(instruction.left);
     Range rightRange = visit(instruction.right);
     if (leftRange == null || rightRange == null) return null;
     BinaryOperation operation = instruction.operation(info.constantSystem);
     return operation.apply(leftRange, rightRange);
   }
 }