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

tests/compiler/dart2js/array_static_intercept_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(a) {
   a.add(42);
   a.removeLast();
   return a.length;
 }
 """;
 
 main() {
   String generated = compile(TEST_ONE, entry: 'foo');
   Expect.isTrue(generated.contains(r'.add$1('));
   Expect.isTrue(generated.contains(r'.removeLast$0('));
-  Expect.isTrue(generated.contains(r'.get$length('));
+  Expect.isTrue(generated.contains(r'.length'));
 }