Fix for computing overridden/implemented members from interfaces.

pkg/analysis_server/lib/src/computer/computer_overrides.dart

Index: pkg/analysis_server/lib/src/computer/computer_overrides.dart
diff --git a/pkg/analysis_server/lib/src/computer/computer_overrides.dart b/pkg/analysis_server/lib/src/computer/computer_overrides.dart
index c47e127ee03903ef743e7066b0ecd51eb2cb3437..9e97df649ccbd018a86df0bc1c62026332cec4f1 100644
--- a/pkg/analysis_server/lib/src/computer/computer_overrides.dart
+++ b/pkg/analysis_server/lib/src/computer/computer_overrides.dart
@@ -45,6 +45,30 @@ class DartUnitOverridesComputer {
     return _overrides;
   }
 
+  void _addInterfaceOverrides(List<engine.Element> elements, String name,
+      engine.InterfaceType type, bool checkType,
+      Set<engine.InterfaceType> visited) {
+    if (type == null) {
+      return;
+    }
+    if (!visited.add(type)) {
+      return;
+    }
+    // check type
+    if (checkType) {
+      engine.Element element = _lookupMember(type.element, name);
+      if (element != null) {
+        elements.add(element);
+      }
+    }
+    // check interfaces
+    for (engine.InterfaceType interfaceType in type.interfaces) {
+      _addInterfaceOverrides(elements, name, interfaceType, true, visited);
+    }
+    // check super
+    _addInterfaceOverrides(elements, name, type.superclass, true, visited);
+  }
+
   void _addOverride(int offset, int length, String name) {
     // super
     engine.Element superEngineElement;
@@ -56,12 +80,10 @@ class DartUnitOverridesComputer {
     }
     // interfaces
     List<engine.Element> interfaceEngineElements = <engine.Element>[];
-    for (engine.InterfaceType interfaceType in _currentClass.interfaces) {
-      engine.ClassElement interfaceElement = interfaceType.element;
-      engine.Element interfaceMember = _lookupMember(interfaceElement, name);
-      if (interfaceMember != null) {
-        interfaceEngineElements.add(interfaceMember);
-      }
+    if (superEngineElement == null) {
+      Set<engine.InterfaceType> visitedTypes = new Set<engine.InterfaceType>();
+      _addInterfaceOverrides(interfaceEngineElements, name, _currentClass.type,
+          false, visitedTypes);
     }
     // is there any override?
     if (superEngineElement != null || interfaceEngineElements.isNotEmpty) {