Add import missing from r45680.

pkg/compiler/lib/src/js_backend/codegen/unsugar.dart

 library dart2js.unsugar_cps;
 
 import '../../cps_ir/cps_ir_nodes.dart';
 
 // TODO(karlklose): share the [ParentVisitor].
 import '../../cps_ir/optimizers.dart';
 import '../../constants/expressions.dart';
 import '../../constants/values.dart';
 import '../../elements/elements.dart' show
     ClassElement,
     FieldElement,
     FunctionElement,
     Local,
     ExecutableElement;
 import '../../js_backend/codegen/glue.dart';
 import '../../dart2jslib.dart' show Selector, World;
+import '../../cps_ir/cps_ir_builder.dart' show ThisParameterLocal;
 
 class ExplicitReceiverParameterEntity implements Local {
   String get name => 'receiver';
   final ExecutableElement executableContext;
   ExplicitReceiverParameterEntity(this.executableContext);
   toString() => 'ExplicitReceiverParameterEntity($executableContext)';
 }
 
 /// Rewrites the initial CPS IR to make Dart semantics explicit and inserts
 /// special nodes that respect JavaScript behavior.
@@ skipping 258 matching lines @@
         new LetPrim(i,
             new Branch(new IsTrue(i),
                 node.trueContinuation.definition,
                 node.falseContinuation.definition)));
     condition.value.unlink();
     node.trueContinuation.unlink();
     node.falseContinuation.unlink();
     parent.body = newNode;
   }
 }