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 1878a37c3221e27c4bf750c76444dd147556fd00..0a47eb1e2ec0077dfb98be59d555fcc51cc8570f 100644
--- a/dart/lib/compiler/implementation/elements/elements.dart
+++ b/dart/lib/compiler/implementation/elements/elements.dart
@@ -216,6 +216,8 @@ class Element implements Hashable {
   bool _isNative = false;
   void setNative() { _isNative = true; }
   bool isNative() => _isNative;
+
+  FunctionElement asFunctionElement() => null;
 }
 
 class ContainerElement extends Element {
@@ -252,12 +254,12 @@ class ContainerElement extends Element {
       }
     } else {
       AbstractFieldElement field = new AbstractFieldElement(element.name, this);
-      addMember(field, listener);
       if (element.kind == ElementKind.GETTER) {
         field.getter = element;
       } else {
         field.setter = element;
       }
+      addMember(field, listener);
     }
   }
 }
@@ -502,11 +504,9 @@ class ForeignElement extends Element {
 class AbstractFieldElement extends Element {
   FunctionElement getter;
   FunctionElement setter;
-  Modifiers modifiers;
 
   AbstractFieldElement(SourceString name, Element enclosing)
-      : super(name, ElementKind.ABSTRACT_FIELD, enclosing),
-        modifiers = new Modifiers.empty();
+      : super(name, ElementKind.ABSTRACT_FIELD, enclosing);
 
   Type computeType(Compiler compiler) {
     throw "internal error: AbstractFieldElement has no type";
@@ -526,11 +526,23 @@ class AbstractFieldElement extends Element {
     // the compilation unit of the abstract element.
     if (getter !== null && getter.enclosingElement === enclosingElement) {
       return getter.position();
-    } else if (setter != null) {
-      // TODO(ahe): checking for null should not be necessary.
+    } else {
       return setter.position();
     }
   }
+
+  Modifiers get modifiers() {
+    // The resolver ensures that the flags match (ignoring abstract).
+    if (getter !== null) {
+      return new Modifiers.withFlags(
+          getter.modifiers.nodes,
+          getter.modifiers.flags | Modifiers.FLAG_ABSTRACT);
+    } else {
+      return new Modifiers.withFlags(
+          setter.modifiers.nodes,
+          setter.modifiers.flags | Modifiers.FLAG_ABSTRACT);
+    }
+  }
 }
 
 class FunctionSignature {
@@ -642,6 +654,8 @@ class FunctionElement extends Element {
   Node parseNode(DiagnosticListener listener) => cachedNode;
 
   Token position() => cachedNode.getBeginToken();
+
+  FunctionElement asFunctionElement() => this;
 }
 
 class ConstructorBodyElement extends FunctionElement {
@@ -735,12 +749,7 @@ class ClassElement extends ContainerElement {
   }
 
   ClassElement ensureResolved(Compiler compiler) {
-    if (!isResolved && !isBeingResolved) {
-      isBeingResolved = true;
-      compiler.resolveClass(this);
-      isBeingResolved = false;
-      isResolved = true;
-    }
+    compiler.resolveClass(this);
     return this;
   }
 
@@ -756,11 +765,12 @@ 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;
   }