Also deal with List.filled in the backend, not just the inferrer and list tracer.

tests/compiler/dart2js/list_tracer_node_type_test.dart

Index: tests/compiler/dart2js/list_tracer_node_type_test.dart
===================================================================
--- tests/compiler/dart2js/list_tracer_node_type_test.dart	(revision 24217)
+++ tests/compiler/dart2js/list_tracer_node_type_test.dart	(working copy)
@@ -29,7 +29,15 @@
 }
 """;
 
+const String TEST4 = r"""
+main() {
+  var a = new List.filled(42, null);
+  a[0] = 42;
+  return a[0] + 42;
+}
+""";
 
+
 main() {
   String generated = compileAll(TEST1);
   // Check that we only do a null check on the receiver for
@@ -45,4 +53,8 @@
   generated = compileAll(TEST3);
   Expect.isFalse(generated.contains('if (typeof t1'));
   Expect.isTrue(generated.contains('if (t1 == null)'));
+
+  generated = compileAll(TEST4);
+  Expect.isFalse(generated.contains('if (typeof t1'));
+  Expect.isTrue(generated.contains('if (t1 == null)'));
 }