Fix static type warnings in language/null_test.

tests/language/null_test.dart

Index: tests/language/null_test.dart
diff --git a/tests/language/null_test.dart b/tests/language/null_test.dart
index 4c1a416a2166570fc2c1dd582fa8e560cb91b19c..c499c50299168a7b3685bbd9254efee0dabcbc22 100644
--- a/tests/language/null_test.dart
+++ b/tests/language/null_test.dart
@@ -37,7 +37,7 @@ class Generic2<T, S> {
 // at compile time. If the result is computed at compile time, the dynamic code
 // will not be tested.
 confuse(x) {
-  try { throw [x]; } catch (e) { return e[0]; }
+  try { throw [x]; } on dynamic catch (e) { return e[0]; }
   return 42;
 }
 
@@ -189,7 +189,7 @@ void test() {
   Expect.equals("null", toString());
   Expect.equals("null", Function.apply(toString, []));
 
-  Expect.throws(() => null.notDeclared());
+  Expect.throws(() => obj.notDeclared());
   var noSuchMethod = null.noSuchMethod;
   // Assing to "var" to prevent warning.
   var capture = new CaptureInvocationMirror();