Ensure that AnalysisContext futures are completed when context disposed.

pkg/analysis_server/test/analysis_server_test.dart

Index: pkg/analysis_server/test/analysis_server_test.dart
diff --git a/pkg/analysis_server/test/analysis_server_test.dart b/pkg/analysis_server/test/analysis_server_test.dart
index 6e7ada51830e301a39fffb4a083cd98dacb032a5..6355ccf35e3de538434fd75b5d34f2d18dcddbe2 100644
--- a/pkg/analysis_server/test/analysis_server_test.dart
+++ b/pkg/analysis_server/test/analysis_server_test.dart
@@ -48,6 +48,19 @@ class AnalysisServerTest {
         rethrowExceptions: true);
   }
 
+  Future test_contextDisposed() {
+    resourceProvider.newFolder('/foo');
+    resourceProvider.newFile('/foo/bar.dart', 'library lib;');
+    server.setAnalysisRoots('0', ['/foo'], [], {});
+    AnalysisContext context;
+    return pumpEventQueue().then((_) {
+      context = server.getAnalysisContext('/foo/bar.dart');
+      server.setAnalysisRoots('1', [], [], {});
+    }).then((_) => pumpEventQueue()).then((_) {
+      expect(context.isDisposed, isTrue);
+    });
+  }
+
   Future test_contextsChangedEvent() {
     resourceProvider.newFolder('/foo');