Bug 1483766 - Use timeout multiplier for Marionette-backed reftests. r=jgraham

timeout_multiplier is set in InternalRefTestImplementation's
constructor but not used.  Instead it appears to only be using the
test's timeout value.

According to the bug report by roc, reftests time out after 10
seconds, when it should be 40.

Thanks-to: Robert O'Callahan <roc@ocallahan.org>

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

@@ -816,11 +816,12 @@ class InternalRefTestImplementation(object):
 
     def run_test(self, test):
         references = self.get_references(test)
+        timeout = (test.timeout * 1000) * self.timeout_multiplier
         rv = self.executor.protocol.marionette._send_message("reftest:run",
                                                              {"test": self.executor.test_url(test),
                                                               "references": references,
                                                               "expected": test.expected(),
-                                                              "timeout": test.timeout * 1000})["value"]
+                                                              "timeout": timeout})["value"]
         return rv
 
     def get_references(self, node):