Add a getNavigation request for plugins

pkg/analyzer_plugin/test/plugin/plugin_test.dart

Index: pkg/analyzer_plugin/test/plugin/plugin_test.dart
diff --git a/pkg/analyzer_plugin/test/plugin/plugin_test.dart b/pkg/analyzer_plugin/test/plugin/plugin_test.dart
index a9dd530de7f4356cab728ba5e5f33746a5e3a892..193e3cff337987e874a788a89fbe8f14a777c4ee 100644
--- a/pkg/analyzer_plugin/test/plugin/plugin_test.dart
+++ b/pkg/analyzer_plugin/test/plugin/plugin_test.dart
@@ -93,6 +93,12 @@ class ServerPluginTest {
     expect(plugin.contextRootContaining(filePath2), isNull);
   }
 
+  test_handleAnalysisGetNavigation() async {
+    var result = await plugin
+        .handleAnalysisGetNavigation(new AnalysisGetNavigationParams('', 1, 2));
+    expect(result, isNotNull);
+  }
+
   test_handleAnalysisHandleWatchEvents() async {
     var result = await plugin.handleAnalysisHandleWatchEvents(
         new AnalysisHandleWatchEventsParams([]));