Migrate test block 47 and downstream dependencies to Dart 2.0.

tests/language_2/checked_null_test.dart

Index: tests/language_2/checked_null_test.dart
diff --git a/tests/language/checked_null_test.dart b/tests/language_2/checked_null_test.dart
similarity index 78%
rename from tests/language/checked_null_test.dart
rename to tests/language_2/checked_null_test.dart
index b86f00ec4b8a7b4514332bbeb1ebda6c08bcd5c1..e69cdd9abf6829640d2896284479bd50e617ee9b 100644
--- a/tests/language/checked_null_test.dart
+++ b/tests/language_2/checked_null_test.dart
@@ -7,8 +7,8 @@ import "package:expect/expect.dart";
 class A {
   Map a;
   Comparator b;
-  // This code exhibited a bug in dart2js checked mode, where the type
-  // of [a] was inferred to be [Comparator] or null;
+  // This code exhibited a bug in dart2js, where the type of [a] was inferred to
+  // be [Comparator] or null;
   A()
       : b = null,
         a = null;
@@ -23,5 +23,5 @@ bar() {
   // receiver type is a typedef. Some code in the dart2js backend were
   // not dealing correctly with typedefs and lead the compiler to
   // crash.
-  new A().a.foo(); //# 01: static type warning
+  new A().a.foo(); //# 01: compile-time error
 }