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

tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart

Index: tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart
diff --git a/tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart b/tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart
index b6fc9ad354a9058b4f04c49cd009ce5abbd59141..b16a1a88966c779b110d0bb770a52b7401162a6e 100644
--- a/tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart
+++ b/tests/compiler/dart2js/js_backend_cps_ir_control_flow_test.dart
@@ -57,11 +57,11 @@ main() {
 }""", """
 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);