[wptrunner] Clear cookies between testharness tests for Chrome (#48106)

Work around #48078 with CDP [0] in the absence of a robust cross-vendor
solution.

[0]: https://chromedevtools.github.io/devtools-protocol/tot/Network/#method-clearBrowserCookies

tools/wptrunner/wptrunner/executors/executorchrome.py

@@ -108,6 +108,9 @@ def close_old_windows(self):
  if not self.reuse_window:
  self.close_test_window()
  self.webdriver.window_handle = self.runner_handle
+ # TODO(web-platform-tests/wpt#48078): Find a cross-platform way to clear
+ # cookies for all domains.
+ self.parent.cdp.execute_cdp_command("Network.clearBrowserCookies")
  return self.runner_handle
 
  def open_test_window(self, window_id):