test_cancel_restart needs the progress notification to show reliably so it can
cancel the pending install. To ensure this a sjs script is used to
asynchronously deliever the XPI data. It starts responding but sends no data
until a second request is made to tell it to complete. So the test can start
the install, then do what it likes with the progress dialog before finally
telling the server to complete the download for the install.
--HG--
extra : rebase_source : 9bd5c617a28ee4edaa8e18599ad8eca0b52f7133
4432095fd7