Bug 1517796 - [wpt] Correctly dismiss user prompts in MarionetteTestharnessProtocolPart._close_windows(). r=jgraham

Using the "Switch To Window" command to check if a user prompt is open
doesn't work because that command doesn't raise a "unexpected alert open"
error. To fix that the "Close Window" command can be used for.

Differential Revision: https://phabricator.services.mozilla.com/D15816

--HG--
extra : moz-landing-system : lando

testing/web-platform/tests/tools/wptrunner/wptrunner/executors/executormarionette.py

@@ -157,10 +157,9 @@ class MarionetteTestharnessProtocolPart(TestharnessProtocolPart):
 
         for handle in handles:
             try:
-                self.dismiss_alert(lambda: self.marionette.switch_to_window(handle))
-                self.marionette.switch_to_window(handle)
                 self.logger.info("Closing window %s" % handle)
-                self.marionette.close()
+                self.marionette.switch_to_window(handle)
+                self.dismiss_alert(lambda: self.marionette.close())
             except errors.NoSuchWindowException:
                 # We might have raced with the previous test to close this
                 # window, skip it.