Move flat_buffer and api_signature into front_end.

pkg/front_end/test/src/base/api_signature_test.dart

Index: pkg/front_end/test/src/base/api_signature_test.dart
diff --git a/pkg/analyzer/test/src/summary/api_signature_test.dart b/pkg/front_end/test/src/base/api_signature_test.dart
similarity index 97%
rename from pkg/analyzer/test/src/summary/api_signature_test.dart
rename to pkg/front_end/test/src/base/api_signature_test.dart
index eb8700b05ee7e944378e120dffae6fba629a71e2..0dbb8468283fec270be7d59ae6af81d7327c7e00 100644
--- a/pkg/analyzer/test/src/summary/api_signature_test.dart
+++ b/pkg/front_end/test/src/base/api_signature_test.dart
@@ -2,12 +2,10 @@
 // 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 test.src.summary.api_signature_test;
-
-import 'package:analyzer/src/summary/api_signature.dart';
 import 'package:analyzer/src/summary/format.dart';
 import 'package:convert/convert.dart';
 import 'package:crypto/crypto.dart';
+import 'package:front_end/src/base/api_signature.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';