[chromedriver] Fix git migration issue and remove svn support from run_buildbot_steps.py

BUG=418590
NOTRY=true

Review URL: https://codereview.chromium.org/615563003

Cr-Commit-Position: refs/heads/master@{#297453}
[ChromeDriver] Detect page loading status when the page is not loaded at all.

BUG=chromedriver:815

Review URL: https://codereview.chromium.org/594383005

Cr-Commit-Position: refs/heads/master@{#297468}