dart2js cps: Fix some analyzer hints in the CPS backend.

pkg/compiler/lib/src/cps_ir/insert_refinements.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 cps_ir.optimization.insert_refinements;
 
 import 'optimizers.dart' show Pass;
 import 'cps_ir_nodes.dart';
 import '../common/names.dart';
 import '../types/types.dart' show TypeMask;
 import 'type_mask_system.dart';
-import 'cps_fragment.dart';
 
 /// Inserts [Refinement] nodes in the IR to allow for sparse path-sensitive
 /// type analysis in the [TypePropagator] pass.
 ///
 /// Refinement nodes are inserted at the arms of a [Branch] node with a
 /// condition of form `x is T` or `x == null`.
 ///
 /// Refinement nodes are inserted after a method invocation to refine the
 /// receiver to the types that can respond to the given selector.
 class InsertRefinements extends TrampolineRecursiveVisitor implements Pass {
@@ skipping 204 matching lines @@
   Expression traverseLetCont(LetCont node) {
     for (Continuation cont in node.continuations) {
       // Do not push the branch continuations here. visitBranch will do that.
       if (!(cont.hasExactlyOneUse && cont.firstRef.parent is Branch)) {
         push(cont);
       }
     }
     return node.body;
   }
 }