[Chromedriver] De-flaky a chromedriver test testActionsMultiTouchPoint

testActionsMultiTouchPoint is flaky, I change the test to wait 50 ms
for the event handler to be executed before checking the length of the
touch events.

Bug: 1011225
Change-Id: I25b16f0c8d5a86959b9b9111c3dbe3ccb2d1ac75
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1846566Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703840}

chrome/test/chromedriver/test/run_py_tests.py

@@ -978,7 +978,13 @@ class ChromeDriverTest(ChromeDriverBaseTestWithWebServer):
       "parameters": {"pointerType": "touch"},
       "id": "pointer2"}]})
     self._driver.PerformActions(actions)
-    events = self._driver.ExecuteScript('return window.events')
+    for _ in range(5):
+      events = self._driver.ExecuteScript('return window.events')
+      if len(events) == 4:
+        break
+      # Wait 10 ms for the event handler to be executed.
+      time.sleep(0.01)
+
     self.assertEquals(4, len(events))
     self.assertEquals("touchstart", events[0]['type'])
     self.assertEquals("touchstart", events[1]['type'])