[ChromeDriver] Implementing tracing support

BUG=

Review URL: https://codereview.chromium.org/454133003

Cr-Commit-Position: refs/heads/master@{#290912}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@290912 0039d316-1c4b-4281-b951-d872f2087c98