Validate cache consistency asynchronously. Compute modification times of physical files in a separa…

pkg/analyzer/lib/file_system/file_system.dart

Index: pkg/analyzer/lib/file_system/file_system.dart
diff --git a/pkg/analyzer/lib/file_system/file_system.dart b/pkg/analyzer/lib/file_system/file_system.dart
index 7a12c6f1cd2d18d2493e1675bde72ff97f2e040f..9fd996a9b7cc3dda98c688af6f6c037a859045f9 100644
--- a/pkg/analyzer/lib/file_system/file_system.dart
+++ b/pkg/analyzer/lib/file_system/file_system.dart
@@ -198,6 +198,11 @@ abstract class ResourceProvider {
   Folder getFolder(String path);
 
   /**
+   * Complete with a list of modification times for the given [sources].
+   */
+  Future<List<int>> getModificationTimes(List<Source> sources);
+
+  /**
    * Return the [Resource] that corresponds to the given [path].
    */
   Resource getResource(String path);
@@ -225,6 +230,8 @@ class ResourceUriResolver extends UriResolver {
 
   ResourceUriResolver(this._provider);
 
+  ResourceProvider get provider => _provider;
+
   @override
   Source resolveAbsolute(Uri uri, [Uri actualUri]) {
     if (!isFileUri(uri)) {
@@ -242,8 +249,6 @@ class ResourceUriResolver extends UriResolver {
   Uri restoreAbsolute(Source source) =>
       _provider.pathContext.toUri(source.fullName);
 
-  ResourceProvider get provider => _provider;
-
   /**
    * Return `true` if the given [uri] is a `file` URI.
    */