Reenable SingleClientDirectorySyncTest.DeleteDirectoryWhenCorrupted

The hope is that https://crrev.com/c/1116549 has resolved the flakiness.
Let's see if it worked :)

Bug: 850980
Change-Id: I12c8832aba6b735179abdeaa220c4634625be326
Reviewed-on: https://chromium-review.googlesource.com/1116780Reviewed-by: Greg Thompson <grt@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570740}

chrome/browser/sync/test/integration/single_client_directory_sync_test.cc

@@ -93,9 +93,8 @@ IN_PROC_BROWSER_TEST_F(SingleClientDirectorySyncTest,
 
 // Verify that when the sync directory's backing store becomes corrupted, we
 // trigger an unrecoverable error and delete the database.
-// Flaky everywhere; see https://crbug.com/850980.
 IN_PROC_BROWSER_TEST_F(SingleClientDirectorySyncTest,
-                       DISABLED_DeleteDirectoryWhenCorrupted) {
+                       DeleteDirectoryWhenCorrupted) {
   ASSERT_TRUE(SetupClients()) << "SetupClients() failed.";
   // Sync and wait for syncing to complete.
   ASSERT_TRUE(SetupSync()) << "SetupSync() failed.";