Bug 1373444 - Look for NoSuchWindowException when waiting for manual browser close in wpt, r=maja_zf

This method works by running a long-running script and catching the exception when
it is interrupted. But the exception changed so we must make a corresponding change here.

MozReview-Commit-ID: EdZZAOVZ0Sw

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

@@ -180,6 +180,9 @@ class MarionetteProtocol(Protocol):
         while True:
             try:
                 self.marionette.execute_async_script("")
+            except errors.NoSuchWindowException:
+                # The window closed
+                break
             except errors.ScriptTimeoutException:
                 self.logger.debug("Script timed out")
                 pass
@@ -187,7 +190,7 @@ class MarionetteProtocol(Protocol):
                 self.logger.debug("Socket closed")
                 break
             except Exception as e:
-                self.logger.error(traceback.format_exc(e))
+                self.logger.warning(traceback.format_exc(e))
                 break
 
     def on_environment_change(self, old_environment, new_environment):