Ignore non-existent analysis roots.

pkg/analysis_server/test/domain_analysis_test.dart

Index: pkg/analysis_server/test/domain_analysis_test.dart
diff --git a/pkg/analysis_server/test/domain_analysis_test.dart b/pkg/analysis_server/test/domain_analysis_test.dart
index d90922b3c6cbce2d70118e748412dcb31f34ae3f..afcff2d95ef404a944250d0fe994980ec817e286 100644
--- a/pkg/analysis_server/test/domain_analysis_test.dart
+++ b/pkg/analysis_server/test/domain_analysis_test.dart
@@ -95,6 +95,18 @@ main() {
             expect(units, hasLength(1));
           });
         });
+
+        test('nonexistent folder', () async {
+          String fileB = '/project_b/b.dart';
+          resourceProvider.newFile(fileB, '// b');
+          var response = testSetAnalysisRoots(['/project_a', '/project_b'], []);
+          var serverRef = server;
+          expect(response, isResponseSuccess('0'));
+          // Non-existence of /project_a should not prevent files in /project_b
+          // from being analyzed.
+          await server.onAnalysisComplete;
+          expect(serverRef.getResolvedCompilationUnits(fileB), hasLength(1));
+        });
       });
     });