Fix forEachOverridePair in the case where the class in question is abstract.

pkg/kernel/lib/class_hierarchy.dart

Index: pkg/kernel/lib/class_hierarchy.dart
diff --git a/pkg/kernel/lib/class_hierarchy.dart b/pkg/kernel/lib/class_hierarchy.dart
index 15f8d7ec0104ba0b4bbf59cf3465fa0b5ce67149..67407748cfee4a9eb303b592d38f733888c8616b 100644
--- a/pkg/kernel/lib/class_hierarchy.dart
+++ b/pkg/kernel/lib/class_hierarchy.dart
@@ -417,20 +417,18 @@ class ClosedWorldClassHierarchy implements ClassHierarchy {
       _reportOverrides(info.declaredSetters, superSetters, callback,
           isSetter: true, onlyAbstract: true);
     }
-    if (!class_.isAbstract) {
-      // If a non-abstract class declares an abstract method M whose
-      // implementation M' is inherited from the superclass, then the inherited
-      // method M' overrides the declared method M.
-      // This flies in the face of conventional override logic, but is necessary
-      // because an instance of the class will contain the method M' which can
-      // be invoked through the interface of M.
-      // Note that [_reportOverrides] does not report self-overrides, so in
-      // most cases these calls will just scan both lists and report nothing.
-      _reportOverrides(info.implementedGettersAndCalls,
-          info.declaredGettersAndCalls, callback);
-      _reportOverrides(info.implementedSetters, info.declaredSetters, callback,
-          isSetter: true);
-    }
+    // If a class declares an abstract method M whose
+    // implementation M' is inherited from the superclass, then the inherited
+    // method M' overrides the declared method M.
+    // This flies in the face of conventional override logic, but is necessary
+    // because an instance of the class will contain the method M' which can
+    // be invoked through the interface of M.
+    // Note that [_reportOverrides] does not report self-overrides, so in
+    // most cases these calls will just scan both lists and report nothing.
+    _reportOverrides(info.implementedGettersAndCalls,
+        info.declaredGettersAndCalls, callback);
+    _reportOverrides(info.implementedSetters, info.declaredSetters, callback,
+        isSetter: true);
   }
 
   @override