Store also 'hasMixinApplication' flag with UnlinkedUnit.

pkg/front_end/test/src/incremental/format_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 'dart:typed_data';
 
 import 'package:front_end/src/base/flat_buffers.dart' as fb;
 import 'package:front_end/src/incremental/format.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
@@ skipping 68 matching lines @@
         2,
         3,
         4
       ], imports: [
         new UnlinkedNamespaceDirectiveBuilder(uri: 'a.dart')
       ], exports: [
         new UnlinkedNamespaceDirectiveBuilder(uri: 'b.dart')
       ], parts: [
         new UnlinkedNamespaceDirectiveBuilder(uri: 'p1.dart'),
         new UnlinkedNamespaceDirectiveBuilder(uri: 'p2.dart'),
-      ]).finish(fbBuilder);
+      ], hasMixinApplication: true)
+          .finish(fbBuilder);
       bytes = fbBuilder.finish(offset);
     }
 
-    var directive = new UnlinkedUnit(bytes);
-    expect(directive.apiSignature, [0, 1, 2, 3, 4]);
+    var unit = new UnlinkedUnit(bytes);
+    expect(unit.apiSignature, [0, 1, 2, 3, 4]);
 
-    expect(directive.imports, hasLength(1));
-    expect(directive.imports[0].uri, 'a.dart');
+    expect(unit.imports, hasLength(1));
+    expect(unit.imports[0].uri, 'a.dart');
 
-    expect(directive.exports, hasLength(1));
-    expect(directive.exports[0].uri, 'b.dart');
+    expect(unit.exports, hasLength(1));
+    expect(unit.exports[0].uri, 'b.dart');
 
-    expect(directive.parts, hasLength(2));
-    expect(directive.parts[0].uri, 'p1.dart');
-    expect(directive.parts[1].uri, 'p2.dart');
+    expect(unit.parts, hasLength(2));
+    expect(unit.parts[0].uri, 'p1.dart');
+    expect(unit.parts[1].uri, 'p2.dart');
+
+    expect(unit.hasMixinApplication, isTrue);
+  }
+
+  void test_UnlinkedUnit_hasMixinApplication_false() {
+    Uint8List bytes;
+    {
+      fb.Builder fbBuilder = new fb.Builder();
+      fb.Offset offset =
+          new UnlinkedUnitBuilder(hasMixinApplication: false).finish(fbBuilder);
+      bytes = fbBuilder.finish(offset);
+    }
+
+    var unit = new UnlinkedUnit(bytes);
+    expect(unit.hasMixinApplication, isFalse);
   }
 }