Move flat_buffer and api_signature into front_end.

pkg/analyzer/lib/src/summary/format.dart

 // Copyright (c) 2015, 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.
 //
 // This file has been automatically generated.  Please do not edit it manually.
 // To regenerate the file, use the script "pkg/analyzer/tool/generate_files".
 
 library analyzer.src.summary.format;
 
-import 'flat_buffers.dart' as fb;
+import 'dart:convert' as convert;
+
+import 'package:front_end/src/base/api_signature.dart' as api_sig;
+import 'package:front_end/src/base/flat_buffers.dart' as fb;
+
 import 'idl.dart' as idl;
-import 'dart:convert' as convert;
-import 'api_signature.dart' as api_sig;
 
 class _EntityRefKindReader extends fb.Reader<idl.EntityRefKind> {
   const _EntityRefKindReader() : super();
 
   @override
   int get size => 1;
 
   @override
   idl.EntityRefKind read(fb.BufferContext bc, int offset) {
     int index = const fb.Uint8Reader().read(bc, offset);
@@ skipping 12628 matching lines @@
         "nameOffset": nameOffset,
         "propagatedTypeSlot": propagatedTypeSlot,
         "type": type,
         "visibleLength": visibleLength,
         "visibleOffset": visibleOffset,
       };
 
   @override
   String toString() => convert.JSON.encode(toJson());
 }