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

pkg/compiler/lib/src/cps_ir/bounds_checker.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.bounds_checker;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart' show Pass;
 import 'octagon.dart';
 import '../constants/values.dart';
 import 'cps_fragment.dart';
 import 'type_mask_system.dart';
 import '../types/types.dart';
 import '../world.dart';
-import '../elements/elements.dart';
 import 'loop_effects.dart';
 import 'effects.dart';
 
 /// Eliminates bounds checks when they can be proven safe.
 ///
 /// In general, this pass will try to eliminate any branch with arithmetic
 /// in the condition, i.e. `x < y`, `x <= y`, `x == y` etc.
 ///
 /// The analysis uses an [Octagon] abstract domain. Unlike traditional octagon
 /// analyzers, we do not use a closed matrix representation, but just maintain
@@ skipping 673 matching lines @@
     }
     return node.body;
   }
 }
 
 /// Lattice representing the known (weak) monotonicity of a loop variable.
 ///
 /// The lattice bottom is represented by `null` and represents the case where
 /// the loop variable never changes value during the loop.
 enum Monotonicity { NotMonotone, Increasing, Decreasing, }