Synchronously invokes the <link linkend="gdbus-method-org-gnome-OnlineAccounts-Manager.
IsSupportedProvider">IsSupportedProvider</link> D-Bus method on this. The calling
thread is blocked until a reply is received.
See call_is_supported_provider for the asynchronous version of this method.
| this |
A ManagerProxy. |
| arg_provider_type |
Argument to pass with the method invocation. |
| out_is_supported |
Return location for return parameter or null to ignore. |
| cancellable |
A Cancellable or null. |
|
true if the call succeeded, false if throws is set. |