(Reland) Start using FileState/FileSystemState to provide consistent view.

pkg/front_end/lib/incremental_kernel_generator.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/src/base/processed_options.dart';
 import 'package:front_end/src/incremental_kernel_generator_impl.dart';
 import 'package:kernel/kernel.dart';
 
@@ skipping 77 matching lines @@
   /// If the future completes successfully, the previous file state is updated
   /// and the set of valid sources is set to the set of all sources in the
   /// program.
   ///
   /// If the future completes with an error (due to errors in the compiled
   /// source code), the caller may consider the previous file state and the set
   /// of valid sources to be unchanged; this means that once the user fixes the
   /// errors, it is safe to call [computeDelta] again.
   Future<DeltaProgram> computeDelta({Future<Null> watch(Uri uri, bool used)});
 
-  /// Remove any source file(s) associated with the given file path from the set
-  /// of valid sources.  This guarantees that those files will be re-read on the
+  /// Remove the file associated with the given file [uri] from the set of
+  /// valid files.  This guarantees that those files will be re-read on the
   /// next call to [computeDelta]).
-  ///
-  /// TODO(scheglov) Update to use URI.
-  void invalidate(String path);
+  void invalidate(Uri uri);
 
   /// Remove all source files from the set of valid sources.  This guarantees
   /// that all files will be re-read on the next call to [computeDelta].
   ///
   /// Note that this does not erase the previous program state; the next time
   /// [computeDelta] is called, if parts of the program are discovered to be
   /// unchanged, parts of the previous program state will still be re-used to
   /// speed up compilation.
   void invalidateAll();
 }