Fix race condition with 'knownFiles'.

pkg/analyzer/test/src/dart/analysis/driver_test.dart

 // Copyright (c) 2016, 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 analyzer.test.driver;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 918 matching lines @@
     expect(driver.knownFiles, contains(a));
     expect(driver.knownFiles, contains(b));
 
     driver.removeFile(a);
 
     // a.dart was removed, but we don't clean up the file state state yet.
     expect(driver.knownFiles, contains(a));
     expect(driver.knownFiles, contains(b));
   }
 
+  test_knownFiles_beforeAnalysis() async {
+    var a = _p('/test/lib/a.dart');
+    var b = _p('/test/lib/b.dart');
+
+    provider.newFile(a, '');
+
+    driver.addFile(a);
+    expect(driver.knownFiles, contains(a));
+    expect(driver.knownFiles, isNot(contains(b)));
+
+    // Remove 'a.dart'.
+    // It has been no analysis yet, so 'a.dart' is not in the file state, only
+    // in 'added' files. So, it disappears when removed.
+    driver.removeFile(a);
+    expect(driver.knownFiles, isNot(contains(a)));
+    expect(driver.knownFiles, isNot(contains(b)));
+  }
+
   test_parseFile_shouldRefresh() async {
     var p = _p('/test/bin/a.dart');
 
     provider.newFile(p, 'class A {}');
     driver.addFile(p);
 
     // Get the result, so force the file reading.
     await driver.getResult(p);
 
     // Update the file.
@@ skipping 482 matching lines @@
   String _p(String path) => provider.convertPath(path);
 
   Future<Null> _waitForIdle() async {
     await idleStatusMonitor.signal;
   }
 
   static String _md5(String content) {
     return hex.encode(md5.convert(UTF8.encode(content)).bytes);
   }
 }