Replace factory constructor with a static method for creating IncrementalKernelGenerator.

pkg/front_end/lib/src/incremental_kernel_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:front_end/file_system.dart';
 import 'package:front_end/incremental_kernel_generator.dart';
 import 'package:front_end/incremental_resolved_ast_generator.dart';
 import 'package:front_end/src/base/processed_options.dart';
@@ skipping 11 matching lines @@
 }
 
 /// Implementation of [IncrementalKernelGenerator].
 ///
 /// TODO(scheglov) Update the documentation.
 ///
 /// Theory of operation: an instance of [IncrementalResolvedAstGenerator] is
 /// used to obtain resolved ASTs, and these are fed into kernel code generation
 /// logic.
 class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
-  /// The URI of the program entry point.
-  final Uri _entryPoint;
-
   /// The compiler options, such as the [FileSystem], the SDK dill location,
   /// etc.
   final ProcessedOptions _options;
 
+  /// The object that knows how to resolve "package:" and "dart:" URIs.
+  final TranslateUri _uriTranslator;
+
+  /// The current file system state.
+  final FileSystemState _fsState;
+
+  /// The URI of the program entry point.
+  final Uri _entryPoint;
+
   /// The set of absolute file URIs that were reported through [invalidate]
   /// and not checked for actual changes yet.
   final Set<Uri> _invalidatedFiles = new Set<Uri>();
 
-  /// The object that knows how to resolve "package:" and "dart:" URIs.
-  TranslateUri _uriTranslator;
-
-  /// The current file system state.
-  FileSystemState _fsState;
-
   /// The cached SDK kernel.
   DillTarget _sdkDillTarget;
 
-  IncrementalKernelGeneratorImpl(this._entryPoint, this._options);
+  IncrementalKernelGeneratorImpl(
+      this._options, this._uriTranslator, this._entryPoint)
+      : _fsState = new FileSystemState(_options.fileSystem, _uriTranslator);
 
   @override
   Future<DeltaProgram> computeDelta(
       {Future<Null> watch(Uri uri, bool used)}) async {
-    await _initialize();
     await _ensureVmLibrariesLoaded();
     await _refreshInvalidatedFiles();
 
     // Ensure that the graph starting at the entry point is ready.
     await _fsState.getFile(_entryPoint);
 
     DillTarget sdkTarget = await _getSdkDillTarget();
     // TODO(scheglov) Use it to also serve other package kernels.
 
     KernelTarget kernelTarget = new KernelTarget(_fsState.fileSystemView,
@@ skipping 40 matching lines @@
       // TODO(scheglov) Read the SDK kernel.
 //      _sdkDillTarget.read(options.sdkSummary);
 //      await _sdkDillTarget.writeOutline(null);
     } else {
 //      Program sdkProgram = _sdkDillTarget.loader.program;
 //      sdkProgram.visitChildren(new _ClearCanonicalNamesVisitor());
     }
     return _sdkDillTarget;
   }
 
-  /// Ensure that asynchronous data from options is ready.
-  ///
-  /// Ideally this data should be prepared in the constructor, but constructors
-  /// cannot be asynchronous.
-  Future<Null> _initialize() async {
-    _uriTranslator ??= await _options.getUriTranslator();
-    _fsState ??= new FileSystemState(_options.fileSystem, _uriTranslator);
-  }
-
   /// Refresh all the invalidated files and update dependencies.
   Future<Null> _refreshInvalidatedFiles() async {
     for (Uri fileUri in _invalidatedFiles) {
       FileState file = await _fsState.getFile(fileUri);
       await file.refresh();
     }
     _invalidatedFiles.clear();
   }
 }
 
 ///// Clears canonical names of [NamedNode] references.
 //class _ClearCanonicalNamesVisitor extends Visitor {
 //  defaultNode(Node node) {
 //    if (node is NamedNode) {
 //      node.reference.canonicalName = null;
 //    }
 //    node.visitChildren(this);
 //  }
 //}