Re-enable flaky NetworkServiceRestartBrowserTest.BrowserIOFactoryAfterStoragePartitionGone

The same issue has been fixed in f8572183.

TBR=kinuko@chromium.org

Bug: 822891
Change-Id: I1f4dcc4e925f315da97b6c7e7ff2278bb1c86564
Reviewed-on: https://chromium-review.googlesource.com/969583Reviewed-by: Chong Zhang <chongz@chromium.org>
Commit-Queue: Chong Zhang <chongz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544176}

content/browser/network_service_restart_browsertest.cc

@@ -565,9 +565,8 @@ IN_PROC_BROWSER_TEST_F(NetworkServiceRestartBrowserTest,
 // Make sure the factory returned from
 // |StoragePartition::GetURLLoaderFactoryForBrowserProcessIOThread()| doesn't
 // crash if it's called after the StoragePartition is deleted.
-// TODO(crbug.com/822891): Disabled since flaky.
 IN_PROC_BROWSER_TEST_F(NetworkServiceRestartBrowserTest,
-                       DISABLED_BrowserIOFactoryAfterStoragePartitionGone) {
+                       BrowserIOFactoryAfterStoragePartitionGone) {
   base::ScopedAllowBlockingForTesting allow_blocking;
   std::unique_ptr<ShellBrowserContext> browser_context =
       std::make_unique<ShellBrowserContext>(true, nullptr);