Support for extensions in chrome.py

Create a Chrome wrapper object.
Add support for loading component extensions by path.
Add a test invoking a private api in telemetry_LoginTest.

BUG=None

TEST=manual

Change-Id: Ice05decb47aeff5bebd445b33306cfc614decd0c
Reviewed-on: https://gerrit.chromium.org/gerrit/62259
Reviewed-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Achuith Bhandarkar <achuith@chromium.org>
Tested-by: Achuith Bhandarkar <achuith@chromium.org>
6 files changed