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- Remove the global unstub_client_mask_ and accordingly make DBusThreadManager::IsUsingStub a non-static function. This makes it obvious when it's ok to call this function (and prevents misuse), namely only after the Manager is initialized.

- By moving the mask to the DBusClientBundle, the cyclic dependency between bundle and manager is broken. The Bundle does not know about the Manager anymore.

- Fix the difference between DBusClientTypeMask ("A set of DBusClients") and DBusClientType ("A single DBusClient").

BUG=408617

Review URL: https://codereview.chromium.org/556833003

Cr-Commit-Position: refs/heads/master@{#294361}