dart2js cps: Retain refinement nodes and update refinements after GVN.

pkg/compiler/lib/src/cps_ir/optimize_interceptors.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.optimize_interceptors;
 
 import 'optimizers.dart';
 import 'cps_ir_nodes.dart';
 import 'loop_hierarchy.dart';
 import 'cps_fragment.dart';
@@ skipping 105 matching lines @@
       interceptor..replaceUsesWith(constantPrim)..destroy();
       let.remove();
     } else if (interceptor.isAlwaysNullOrIntercepted) {
       Primitive input = interceptor.input.definition;
       Primitive constantPrim = makeConstantFor(constant,
           useSite: let,
           type: interceptor.type.nonNullable(),
           sourceInformation: interceptor.sourceInformation);
       CpsFragment cps = new CpsFragment(interceptor.sourceInformation);
       Parameter param = new Parameter(interceptor.hint);
+      param.type = interceptor.type;
       Continuation cont = cps.letCont(<Parameter>[param]);
       if (interceptor.interceptedClasses.every(hasNoFalsyValues)) {
         // If null is the only falsy value, compile as "x && CONST".
         cps.ifFalsy(input).invokeContinuation(cont, [input]);
       } else {
         // If there are other falsy values compile as "x == null ? x : CONST".
         Primitive condition = cps.applyBuiltin(
             BuiltinOperator.LooseEq,
             [input, cps.makeNull()]);
         cps.ifTruthy(condition).invokeContinuation(cont, [input]);
@@ skipping 42 matching lines @@
         sharedConstantFor.remove(prim.value);
       });
     }
     return next;
   }
 
   bool shouldShareConstant(Constant constant) {
     return constant.value.isInterceptor;
   }
 }