Remove special casing of == null

tests/compiler/dart2js/kernel/compile_from_dill_test.dart

Index: tests/compiler/dart2js/kernel/compile_from_dill_test.dart
diff --git a/tests/compiler/dart2js/kernel/compile_from_dill_test.dart b/tests/compiler/dart2js/kernel/compile_from_dill_test.dart
index 22bd53a8605f772a129ff61869c8660c81805c7a..4c88712bb59de4001f45a79751118363bf8f78c7 100644
--- a/tests/compiler/dart2js/kernel/compile_from_dill_test.dart
+++ b/tests/compiler/dart2js/kernel/compile_from_dill_test.dart
@@ -49,10 +49,15 @@ main() {
   new Class('');
   Class.staticField;
   var x = null;
+  var y1 = x == null;
+  var y2 = null == x;
+  var z = x?.toString();
+  var w = x == null ? null : x.toString();

[Siggi Cherem (dart-lang), 2017/06/23 20:43:37]

with your change, is `x ?? y` and `x ??= y` handled as well?

[Johnni Winther, 2017/06/26 10:47:40]

Yes. Tests added.

   for (int i = 0; i < 10; i++) {
     x = i;
     if (i == 5) break;
   }
+  print(x);
   return x;
 }
 '''