Encode super calls via extra properties on prototypes.

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index dfd5a92a974849f20cdaecc6a8e44d7428143636..ee38cac2d3811bac63562f0ac7b017c487b67603 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -323,6 +323,12 @@ class JavaScriptBackend extends Backend {
    */
   final Set<ClassElement> specialOperatorEqClasses = new Set<ClassElement>();
 
+  /**
+   * A Map from classes to the members of superclasses they call via super.
+   */
+  final Map<ClassElement, Set<Element>> aliasedSuperMembers =
+      new Map<ClassElement, Set<Element>>();
+
   List<CompilerTask> get tasks {
     return <CompilerTask>[builder, optimizer, generator, emitter];
   }
@@ -528,6 +534,18 @@ class JavaScriptBackend extends Backend {
     return name;
   }
 
+  void registerAliasedSuperMember(Element method, ClassElement caller) {
+    Set<Element> methods =
+        aliasedSuperMembers.putIfAbsent(caller, () => new Setlet<Element>());
+    methods.add(method);
+  }
+
+  Set<Element> getAliasedSuperMembers(ClassElement subclass) {
+    Set<Element> aliases = aliasedSuperMembers[subclass];
+    if (aliases == null) return const ImmutableEmptySet<Element>();
+    return aliases;
+  }
+
   bool isInterceptedMethod(Element element) {
     if (!element.isInstanceMember) return false;
     if (element.isGenerativeConstructorBody) {