Disable flaky test ExtensionSettingsApiTest.ManagedStorageEvents.

This test is failing quite a bit on Linux Aura.

BUG=321448
TBR=kalman@chromium.org

Review URL: https://codereview.chromium.org/77223003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236128 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236128