Use index in J/KTypeVariable and fix remaining inequivalence

pkg/compiler/lib/src/common_elements.dart

Index: pkg/compiler/lib/src/common_elements.dart
diff --git a/pkg/compiler/lib/src/common_elements.dart b/pkg/compiler/lib/src/common_elements.dart
index 379e9c8ba2922db9ee8ba59b4a985287c5009780..580935ed9c6c8cae97da7357fa2eabdefaedd99d 100644
--- a/pkg/compiler/lib/src/common_elements.dart
+++ b/pkg/compiler/lib/src/common_elements.dart
@@ -5,6 +5,7 @@
 // TODO(sigmund): rename and move to common/elements.dart
 library dart2js.type_system;
 
+import 'common.dart';
 import 'common/names.dart' show Identifiers, Uris;
 import 'constants/values.dart';
 import 'elements/entities.dart';
@@ -1161,6 +1162,17 @@ class CommonElements {
     _ensureExpectAnnotations();
     return _expectAssumeDynamicClass;
   }
+
+  /// Returns `true` if the implementation of the 'operator ==' [function] is
+  /// known to handle `null` as argument.
+  bool operatorEqHandlesNullArgument(FunctionEntity function) {
+    assert(function.name == '==',
+        failedAt(function, "Unexpected function $function."));
+    ClassEntity cls = function.enclosingClass;
+    return cls == objectClass ||
+        cls == jsInterceptorClass ||
+        cls == jsNullClass;
+  }
 }
 
 /// Interface for accessing libraries, classes and members.