Ignore file system errors when deleting analysis server index dir.

pkg/analysis_services/lib/src/index/store/temporary_folder_file_manager.dart

Index: pkg/analysis_services/lib/src/index/store/temporary_folder_file_manager.dart
diff --git a/pkg/analysis_services/lib/src/index/store/temporary_folder_file_manager.dart b/pkg/analysis_services/lib/src/index/store/temporary_folder_file_manager.dart
index 1e30417d0d3253358d44fb187400bef46b0f62a4..331da600638d3557027f2d3674df9f4ea63d600e 100644
--- a/pkg/analysis_services/lib/src/index/store/temporary_folder_file_manager.dart
+++ b/pkg/analysis_services/lib/src/index/store/temporary_folder_file_manager.dart
@@ -23,7 +23,19 @@ class TemporaryFolderFileManager implements FileManager {
   @override
   void clear() {
     if (_directory != null) {
-      _directory.deleteSync(recursive: true);
+      try {
+        _directory.deleteSync(recursive: true);
+      } on FileSystemException {
+        // For some reason, on Windows this sometimes results in the error:
+        // "FileSystemException: Deletion failed, path = '...' (OS Error: The
+        // process cannot access the file because it is being used by another
+        // process., errno = 32).  (Speculation: perhaps createTempSync is not
+        // successfully creating a unique name, so multiple processes are
+        // trying to access the same file?)
+        //
+        // For now, work around the problem by ignoring the exception.
+        // TODO(paulberry): fix the actual root cause of this bug.
+      }
       _directory = null;
     }
   }