Implement override checks.

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 db285be7446542d499059f2cc318fb3d2e1c4d9e..ef4e7c4443ed63b98697269702690d0e6dd97331 100644
--- a/dart/lib/compiler/implementation/elements/elements.dart
+++ b/dart/lib/compiler/implementation/elements/elements.dart
@@ -214,6 +214,8 @@ class Element implements Hashable {
   bool _isNative = false;
   void setNative() { _isNative = true; }
   bool isNative() => _isNative;
+
+  FunctionElement asFunctionElement() => null;
 }
 
 class ContainerElement extends Element {
@@ -640,6 +642,8 @@ class FunctionElement extends Element {
   Node parseNode(DiagnosticListener listener) => cachedNode;
 
   Token position() => cachedNode.getBeginToken();
+
+  FunctionElement asFunctionElement() => this;
 }
 
 class ConstructorBodyElement extends FunctionElement {
@@ -754,11 +758,12 @@ class ClassElement extends ContainerElement {
   Element lookupSuperMember(SourceString memberName) {
     for (ClassElement s = superclass; s != null; s = s.superclass) {
       Element e = s.lookupLocalMember(memberName);
-      if (e !== null) {
-        if (!memberName.isPrivate() || getLibrary() === e.getLibrary()) {
-          return e;
-        }
-      }
+      if (e === null) continue;
+      // Private members from a different library are not visible.
+      if (memberName.isPrivate() && getLibrary() !== e.getLibrary()) continue;
+      // Static members are not inherited.
+      if (e.modifiers.isStatic()) continue;
+      return e;
     }
     return null;
   }