Revert "Extend file-system abstraction with a couple methods, remove context."

pkg/front_end/lib/memory_file_system.dart

Index: pkg/front_end/lib/memory_file_system.dart
diff --git a/pkg/front_end/lib/memory_file_system.dart b/pkg/front_end/lib/memory_file_system.dart
index 6c57167a87d45e1620fadab02a82fe585658256d..e7382adfb38a38d51b534894d9c7ce6de27d1a25 100644
--- a/pkg/front_end/lib/memory_file_system.dart
+++ b/pkg/front_end/lib/memory_file_system.dart
@@ -8,6 +8,8 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:typed_data';
 
+import 'package:path/path.dart' as p;
+
 import 'file_system.dart';
 
 /// Concrete implementation of [FileSystem] which performs its operations on an
@@ -15,13 +17,10 @@ import 'file_system.dart';
 ///
 /// Not intended to be implemented or extended by clients.
 class MemoryFileSystem implements FileSystem {
-  final Map<Uri, Uint8List> _files = {};
-  final Map<Uri, DateTime> _lastModified = {};
+  @override
+  final p.Context context;
 
-  // Counter used to create mock last-modification timestamps. The memory
-  // file-system is mainly used for testing, so we use mock timestamps to avoid
-  // introducing non-determinism.
-  int _lastUpdate = 0;
+  final Map<Uri, Uint8List> _files = {};
 
   /// The "current directory" in the in-memory virtual file system.
   ///
@@ -30,7 +29,7 @@ class MemoryFileSystem implements FileSystem {
   /// Always ends in a trailing '/'.
   Uri currentDirectory;
 
-  MemoryFileSystem(Uri currentDirectory)
+  MemoryFileSystem(this.context, Uri currentDirectory)
       : currentDirectory = _addTrailingSlash(currentDirectory);
 
   @override
@@ -81,24 +80,12 @@ class MemoryFileSystemEntity implements FileSystemEntity {
     return UTF8.decode(contents);
   }
 
-  @override
-  Future<bool> exists() async => _fileSystem._files[uri] != null;
-
-  @override
-  Future<DateTime> lastModified() async {
-    var lastModified = _fileSystem._lastModified[uri];
-    if (lastModified == null) {
-      throw new Exception('File does not exist');
-    }
-    return lastModified;
-  }
-
   /// Writes the given raw bytes to this file system entity.
   ///
   /// If no file exists, one is created.  If a file exists already, it is
   /// overwritten.
   void writeAsBytesSync(List<int> bytes) {
-    _update(uri, new Uint8List.fromList(bytes));
+    _fileSystem._files[uri] = new Uint8List.fromList(bytes);
   }
 
   /// Writes the given string to this file system entity.
@@ -111,12 +98,6 @@ class MemoryFileSystemEntity implements FileSystemEntity {
     // Note: the return type of UTF8.encode is List<int>, but in practice it
     // always returns Uint8List.  We rely on that for efficiency, so that we
     // don't have to make an extra copy.
-    _update(uri, UTF8.encode(s) as Uint8List);
-  }
-
-  void _update(Uri uri, Uint8List data) {
-    _fileSystem._files[uri] = data;
-    _fileSystem._lastModified[uri] =
-        new DateTime.fromMicrosecondsSinceEpoch(++_fileSystem._lastUpdate);
+    _fileSystem._files[uri] = UTF8.encode(s) as Uint8List;
   }
 }