Update SOURCE_KIND when a missing source file appears

pkg/analyzer/test/generated/compile_time_error_code_test.dart

 // Copyright (c) 2014, 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.generated.compile_time_error_code_test;
 
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/parser.dart' show ParserErrorCode;
 import 'package:analyzer/src/generated/source_io.dart';
+import 'package:unittest/unittest.dart' show expect;
 
 import '../reflective_tests.dart';
 import '../utils.dart';
 import 'resolver_test.dart';
 
 main() {
   initializeTestEnvironment();
   runReflectiveTests(CompileTimeErrorCodeTest);
 }
 
@@ skipping 6016 matching lines @@
     computeLibrarySourceErrors(source);
     assertErrors(source, [CompileTimeErrorCode.URI_DOES_NOT_EXIST]);
   }
 
   void test_uriDoesNotExist_import() {
     Source source = addSource("import 'unknown.dart';");
     computeLibrarySourceErrors(source);
     assertErrors(source, [CompileTimeErrorCode.URI_DOES_NOT_EXIST]);
   }
 
+  void test_uriDoesNotExist_import_then_fixed() {
+    Source source = addSource("import 'target.dart';");
+    computeLibrarySourceErrors(source);
+    assertErrors(source, [CompileTimeErrorCode.URI_DOES_NOT_EXIST]);
+
+    // Check that the file is represented as missing.
+    Source target =
+        analysisContext2.getSourcesWithFullName("/target.dart").first;
+    expect(analysisContext2.getModificationStamp(target), -1);
+
+    // Add an overlay in the same way as AnalysisServer.
+    analysisContext2
+      ..setContents(target, "")
+      ..handleContentsChanged(target, null, "", true);
+
+    // Make sure the error goes away.
+    // TODO(skybrian) why isn't there an unused import hint?
+    computeLibrarySourceErrors(source);
+    assertErrors(source, [HintCode.UNUSED_IMPORT]);
+  }
+
   void test_uriDoesNotExist_part() {
     Source source = addSource(r'''
 library lib;
 part 'unknown.dart';''');
     computeLibrarySourceErrors(source);
     assertErrors(source, [CompileTimeErrorCode.URI_DOES_NOT_EXIST]);
   }
 
   void test_uriWithInterpolation_constant() {
     Source source = addSource("import 'stuff_\$platform.dart';");
@@ skipping 228 matching lines @@
         source, [CompileTimeErrorCode.WRONG_NUMBER_OF_PARAMETERS_FOR_OPERATOR]);
     verify([source]);
     reset();
   }
 
   void _check_wrongNumberOfParametersForOperator1(String name) {
     _check_wrongNumberOfParametersForOperator(name, "");
     _check_wrongNumberOfParametersForOperator(name, "a, b");
   }
 }