[Extensions] Re-enable an IsolatedAppTest test.

This test was disabled a long time ago, with a comment that
it was broken by a related change. This test seems to work now,
so I've enabled it. The related bugs seem to indicate the
feature is no longer planned, so perhaps this test be removed,
per the comment, if it's not really testing anything worthwhile.

Bug: 159932
Change-Id: I36950024b8448c56e669c371380a3daf450e96f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2414772Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: David Bertoni <dbertoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809568}

chrome/browser/extensions/isolated_app_browsertest.cc

@@ -528,12 +528,7 @@ IN_PROC_BROWSER_TEST_F(IsolatedAppTest, MAYBE_IsolatedAppProcessModel) {
                               ->GetID());
 }
 
-// This test no longer passes, since we don't properly isolate sessionStorage
-// for isolated apps. This was broken as part of the changes for storage
-// partition support for webview tags.
-// TODO(nasko): If isolated apps is no longer developed, this test should be
-// removed. http://crbug.com/159932
-IN_PROC_BROWSER_TEST_F(IsolatedAppTest, DISABLED_SessionStorage) {
+IN_PROC_BROWSER_TEST_F(IsolatedAppTest, SessionStorage) {
   ASSERT_TRUE(embedded_test_server()->Start());
 
   ASSERT_TRUE(LoadExtension(test_data_dir_.AppendASCII("isolated_apps/app1")));