Check overrides.

dart/lib/compiler/implementation/elements/elements.dart

Index: dart/lib/compiler/implementation/elements/elements.dart
diff --git a/dart/lib/compiler/implementation/elements/elements.dart b/dart/lib/compiler/implementation/elements/elements.dart
index 03895b2087442c5c6508b957b756e0c79043ea58..f111cd254a84bca80cfca2ca26d5131676e4af59 100644
--- a/dart/lib/compiler/implementation/elements/elements.dart
+++ b/dart/lib/compiler/implementation/elements/elements.dart
@@ -275,6 +275,10 @@ class Element implements Hashable {
   Element cloneTo(Element enclosing, DiagnosticListener listener) {
     listener.cancel("Unimplemented cloneTo", element: this);
   }
+
+  Link<Type> get allSupertypesAndSelf() {
+    return allSupertypes.prepend(new InterfaceType(this));
+  }
 }
 
 class ContainerElement extends Element {
@@ -1075,9 +1079,25 @@ class ClassElement extends ContainerElement
       if (e.modifiers.isStatic()) continue;
       return e;
     }
+    if (isInterface()) {
+      return lookupSuperInterfaceMember(memberName, getLibrary());
+    }
     return null;
   }
 
+  Element lookupSuperInterfaceMember(SourceString memberName,
+                                     LibraryElement fromLibrary) {
+    for (Type t in interfaces) {
+      Element e = t.element.lookupLocalMember(memberName);
+      if (e === null) continue;
+      // Private members from a different library are not visible.
+      if (memberName.isPrivate() && fromLibrary !== e.getLibrary()) continue;

[karlklose, 2012/08/14 11:06:51]

You could store the result of memberName.isPrivate() in a local outside the
loop.

[ahe, 2012/08/14 18:20:34]

Done.

+      // Static members are not inherited.
+      if (e.modifiers.isStatic()) continue;
+      return e;
+    }
+  }

[karlklose, 2012/08/14 11:06:51]

I would prefer an explicit 'return null' here.

[ahe, 2012/08/14 18:20:34]

Done.

+
   /**
    * Find the first member in the class chain with the given
    * [memberName]. This method is NOT to be used for resolving