Expose getter and setter invocations by name, in dart2js 'World'.

pkg/compiler/lib/src/universe/universe.dart

Index: pkg/compiler/lib/src/universe/universe.dart
diff --git a/pkg/compiler/lib/src/universe/universe.dart b/pkg/compiler/lib/src/universe/universe.dart
index 28715e6ddba336b3e180fc36065124cf2f6bd00f..aa90f73fca182335f047d30a87b85a457681bcb2 100644
--- a/pkg/compiler/lib/src/universe/universe.dart
+++ b/pkg/compiler/lib/src/universe/universe.dart
@@ -4,6 +4,8 @@
 
 library universe;
 
+import 'dart:collection';
+
 import '../elements/elements.dart';
 import '../dart2jslib.dart';
 import '../dart_types.dart';
@@ -277,8 +279,21 @@ class Universe {
     return masks.add(mask);
   }
 
+  Map<Selector, TypeMaskSet> _asUnmodifiable(Map<Selector, TypeMaskSet> map) {
+    if (map == null) return null;
+    return new UnmodifiableMapView(map);
+  }
+
   Map<Selector, TypeMaskSet> invocationsByName(String name) {
-    return _invokedNames[name];
+    return _asUnmodifiable(_invokedNames[name]);
+  }
+
+  Map<Selector, TypeMaskSet> getterInvocationsByName(String name) {
+    return _asUnmodifiable(_invokedGetters[name]);
+  }
+
+  Map<Selector, TypeMaskSet> setterInvocationsByName(String name) {
+    return _asUnmodifiable(_invokedSetters[name]);
   }
 
   void forEachInvokedName(