Add support for multi-roots

pkg/front_end/test/summary_generator_test.dart

 // Copyright (c) 2017, 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 'package:front_end/front_end.dart';
 import 'package:front_end/src/testing/compiler_common.dart';
 import 'package:kernel/ast.dart';
 import 'package:kernel/kernel.dart';
 
 import 'package:test/test.dart';
@@ skipping 93 matching lines @@
     var errors = [];
     var options = new CompilerOptions()..onError = (e) => errors.add(e);
     await summarize(['b.dart'], allSources, options: options);
     expect(errors.first.toString(), contains('Invalid access'));
     errors.clear();
 
     await summarize(['a.dart', 'b.dart'], allSources, options: options);
     expect(errors, isEmpty);
   });
 
+  test('summarization with multi-roots can work hermetically', () async {
+    var errors = [];
+    var options = new CompilerOptions()
+      ..onError = ((e) => errors.add(e))
+      ..multiRoots = [toTestUri('rootA/'), toTestUri('rootB/')];
+
+    var multiRootSources = <String, String>{
+      'rootA/a.dart': allSources['a.dart'],
+      'rootB/b.dart': allSources['b.dart'],
+    };
+
+    await summarize(['multi-root:/b.dart'], multiRootSources, options: options);
+    expect(errors.first.toString(), contains('Invalid access'));
+    errors.clear();
+
+    await summarize(
+        ['multi-root:/a.dart', 'multi-root:/b.dart'], multiRootSources,
+        options: options);
+    expect(errors, isEmpty);
+  });
+
   // TODO(sigmund): test trimDependencies when it is part of the public API.
 }
 
 var allSources = {
   'a.dart': 'class A { foo() { print("hi"); } }',
   'b.dart': 'import "a.dart"; class B extends A {}',
   'c.dart': 'class C { bar() => 1; }',
   'd.dart': '''
       import "a.dart";
       import "b.dart";
@@ skipping 19 matching lines @@
   var aClass = aLib.classes.firstWhere((c) => c.name == 'A');
   var bClass = bLib.classes.firstWhere((c) => c.name == 'B');
   expect(bClass.superclass, same(aClass));
 
   var dClass = dLib.classes.firstWhere((c) => c.name == 'D');
   expect(dClass.superclass.superclass, same(bClass));
 
   var dInterface = dClass.implementedTypes.first.classNode;
   expect(dInterface, same(aClass));
 }