A request observer proxy is used to ship data over to another thread
specified by the thread’s dispatch target. The “true” request observer’s
methods are invoked on the other thread.
This interface only provides the initialization needed after construction.
Otherwise, these objects are used simply as nsIRequestObserver’s.
Initializes an nsIRequestObserverProxy.
| observer | - receives observer notifications on the main thread |
| context | - the context argument that will be passed to OnStopRequest and OnStartRequest. This has to be stored permanently on initialization because it sometimes can't be AddRef/Release'd off-main-thread. |