[ChromeDriver] Use blinkpy's method to get Webdriver test expectations

Instead of using typ's methods to get the test expectations, we should
use blinkpy's methods.

Bug: 986447
Change-Id: I58508a44536ccc73864c1acd10c2be06af82a3a6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2067377Reviewed-by: John Chen <johnchen@chromium.org>
Reviewed-by: Rakib Hasan <rmhasan@google.com>
Commit-Queue: Rakib Hasan <rmhasan@google.com>
Cr-Commit-Position: refs/heads/master@{#743217}

chrome/test/chromedriver/test/run_webdriver_tests.py

@@ -348,8 +348,7 @@ if __name__ == '__main__':
     success_count = 0
 
     for test_result in test_results:
-      exp = webdriver_expectations.expectations[0].expectations_for(
-          test_result.test_name)
+      exp = webdriver_expectations.get_expectations(test_result.test_name)
       expected_result = ' '.join(exp.results)
       is_unexpected = test_result.test_status not in exp.results