Move resolveRelativeUri into front_end.

pkg/front_end/lib/src/incremental_resolved_ast_generator_impl.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:async';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/context/context.dart';
 import 'package:analyzer/src/dart/analysis/byte_store.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart' as driver;
 import 'package:analyzer/src/dart/analysis/file_state.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source.dart';
-import 'package:analyzer/src/generated/utilities_dart.dart';
 import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/util/absolute_path.dart';
 import 'package:front_end/incremental_resolved_ast_generator.dart';
 import 'package:front_end/src/base/file_repository.dart';
 import 'package:front_end/src/base/processed_options.dart';
+import 'package:front_end/src/base/resolve_relative_uri.dart';
 import 'package:front_end/src/base/source.dart';
 import 'package:front_end/src/dependency_grapher_impl.dart';
 import 'package:path/src/context.dart';
 
 dynamic unimplemented() {
   // TODO(paulberry): get rid of this.
   throw new UnimplementedError();
 }
 
 /// Implementation of [IncrementalKernelGenerator].
@@ skipping 263 matching lines @@
 class _SourceProxy extends BasicSource {
   @override
   final String fullName;
 
   _SourceProxy(Uri uri, this.fullName) : super(uri);
 
   int get modificationStamp => 0;
 
   noSuchMethod(Invocation invocation) => unimplemented();
 }