Issue 29968. When a file is added, and it is already known, refresh it.

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.
 
 import 'dart:async';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_resolution_map.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 1643 matching lines @@
 
     Future<AnalysisResult> resultFuture = driver.getResult(testFile);
     driver.removeFile(testFile);
 
     AnalysisResult result = await resultFuture;
     expect(result, isNotNull);
     expect(result.path, testFile);
     expect(result.unit, isNotNull);
   }
 
+  test_getResult_importLibrary_thenRemoveIt() async {
+    var a = _p('/test/lib/a.dart');
+    var b = _p('/test/lib/b.dart');
+    provider.newFile(a, 'class A {}');
+    provider.newFile(
+        b,
+        r'''
+import 'a.dart';
+class B extends A {}
+''');
+
+    driver.addFile(a);
+    driver.addFile(b);
+    await scheduler.waitForIdle();
+
+    // No errors in b.dart
+    {
+      AnalysisResult result = await driver.getResult(b);
+      expect(result.errors, isEmpty);
+    }
+
+    // Remove a.dart and reanalyze.
+    provider.deleteFile(a);
+    driver.removeFile(a);
+
+    // The unresolved URI error must be reported.
+    {
+      AnalysisResult result = await driver.getResult(b);
+      expect(
+          result.errors,
+          contains(predicate((AnalysisError e) =>
+              e.errorCode == CompileTimeErrorCode.URI_DOES_NOT_EXIST)));
+    }
+
+    // Restore a.dart and reanalyze.
+    provider.newFile(a, 'class A {}');
+    driver.addFile(a);
+
+    // No errors in b.dart again.
+    {
+      AnalysisResult result = await driver.getResult(b);
+      expect(result.errors, isEmpty);
+    }
+  }
+
   test_getResult_twoPendingFutures() async {
     String content = 'main() {}';
     addTestFile(content, priority: true);
 
     Future<AnalysisResult> future1 = driver.getResult(testFile);
     Future<AnalysisResult> future2 = driver.getResult(testFile);
 
     // Both futures complete, with the same result.
     AnalysisResult result1 = await future1;
     AnalysisResult result2 = await future2;
@@ skipping 1126 matching lines @@
     var path = _p('/test.dart');
     expect(() {
       driver.removeFile(path);
     }, throwsStateError);
   }
 
   String _p(String path) => provider.convertPath(path);
 }
 
 class _SourceMock extends TypedMock implements Source {}