dart2js cps: Ensure JSArray is emitted when we see a type cast.

tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart

 // Copyright (c) 2014, 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.
 
 // Tests of control flow statements.
 
 library control_flow_tests;
 
 import 'js_backend_cps_ir.dart';
 
@@ skipping 39 matching lines @@
 
 main() {
   for (int i = 0; foo(true); i = foo(i)) {
     print(1);
     if (foo(false)) break;
   }
   print(2);
 }""", """
 function() {
   var i = 0;
-  L1:
+  L2:
     while (P.identical(V.foo(true), true)) {
       P.print(1);
       if (P.identical(V.foo(false), true))
-        break L1;
+        break L2;

[asgerf, 2015/07/03 12:00:34]

Reason for change: 
Labels are currently numbered globally (we should fix that).

Another label seems to get emitted because of the dependency:
print -> H.S -> type test -> list -> [...] -> StringBuffer.writeAll

       i = V.foo(i);
     }
   P.print(2);
 }"""),
 const TestEntry("""
 foo(a) => a;
 
 main() {
  if (foo(true)) {
    print(1);
@@ skipping 51 matching lines @@
 }""","""
 function() {
   V.foo();
   P.print("good");
 }"""),
 ];
 
 void main() {
   runTests(tests);
 }