After a dynamic call, refine the receiver type by looking at the potential targets of that call.

tests/compiler/dart2js/code_motion_test.dart

 // Copyright (c) 2011, 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.
 
 import "package:expect/expect.dart";
 import 'compiler_helper.dart';
 
 const String TEST_ONE = r"""
-foo(int a, int b, bool param2) {
+foo(int a, bool param2) {
   for (int i = 0; i < 1; i++) {
     var x = a + 5;  // '+' is now GVNed.
     if (param2) {
-      print(a + b);
+      print(a + 42);
     } else {
-      print(a + b);
+      print(a + 42);
     }
   }
 }
 """;
 
 main() {
   String generated = compile(TEST_ONE, entry: 'foo');
-  RegExp regexp = new RegExp('a \\+ b');
+  RegExp regexp = new RegExp('a \\+ 42');
   Iterator matches = regexp.allMatches(generated).iterator;
   Expect.isTrue(matches.moveNext());
   Expect.isFalse(matches.moveNext());
 }