Initializes the transfer with certain properties. This function must
be called prior to accessing any properties on this interface.
| aSource | The source URI of the transfer. Must not be null. |
| aTarget | The target URI of the transfer. Must not be null. |
| aDisplayName | The user-readable description of the transfer. Can be empty. |
| aMIMEInfo | The MIME info associated with the target, including MIME type and helper app when appropriate. This parameter is optional. |
| startTime | Time when the download started (ie, when the first response from the server was received) XXX presumably wbp and exthandler do this differently |
| aTempFile | The location of a temporary file; i.e. a file in which the received data will be stored, but which is not equal to the target file. (will be moved to the real target by the caller, when the download is finished) May be null. |
| aCancelable | An object that can be used to abort the download. Must not be null. Implementations are expected to hold a strong reference to this object until the download is finished, at which point they should release the reference. |
| aIsPrivate | Used to determine the privacy status of the new transfer. If true, indicates that the transfer was initiated from a source that desires privacy. |