When doing SSA type propagation, refine the receiver after a call.

sdk/lib/_internal/compiler/implementation/ssa/nodes.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.
 
 part of ssa;
 
 abstract class HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
@@ skipping 1220 matching lines @@
   bool get isInterceptedCall {
     // We know it's a selector call if it follows the interceptor
     // calling convention, which adds the actual receiver as a
     // parameter to the call.
     return (selector != null) && (inputs.length - 2 == selector.argumentCount);
   }
 }
 
 abstract class HInvokeDynamic extends HInvoke {
   final InvokeDynamicSpecializer specializer;
-  final Selector selector;
+  Selector selector;
   Element element;
 
   HInvokeDynamic(Selector selector,
                  this.element,
                  List<HInstruction> inputs,
                  [bool isIntercepted = false])
     : super(inputs),
       this.selector = selector,
       specializer = isIntercepted
           ? InvokeDynamicSpecializer.lookupSpecializer(selector)
@@ skipping 1483 matching lines @@
   HBasicBlock get start => expression.start;
   HBasicBlock get end {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty);
     return statements.last.end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }