Implement override checks for methods.

pkg/front_end/lib/src/fasta/analyzer/analyzer_loader.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.analyzer_loader;
 
 import 'package:kernel/ast.dart' show Program;
 
 import '../builder/builder.dart' show LibraryBuilder;
 
 import '../target_implementation.dart' show TargetImplementation;
 
+import '../source/source_class_builder.dart' show SourceClassBuilder;
+
 import '../source/source_loader.dart' show SourceLoader;
 
 import 'element_store.dart' show ElementStore;
 
 import 'analyzer_diet_listener.dart' show AnalyzerDietListener;
 
 class AnalyzerLoader<L> extends SourceLoader<L> {
   ElementStore elementStore;
 
   AnalyzerLoader(TargetImplementation target) : super(target);
 
   @override
   void computeHierarchy(Program program) {
     elementStore = new ElementStore(coreLibrary, builders);
     ticker.logMs("Built analyzer element model.");
   }
 
   @override
   AnalyzerDietListener createDietListener(LibraryBuilder library) {
     return new AnalyzerDietListener(library, elementStore);
   }
+
+  @override
+  void checkOverrides(List<SourceClassBuilder> sourceClasses) {
+    // Not implemented yet. Requires [hierarchy].
+  }
 }