Allow tests to identify the TestPlatform they are being run on.

I am working on an in-browser/webdriver hybrid testing method. This requires exposing a WebDriver API from the test server for each browser. From within the test, I need to know which of those WebDriver sessions to connect to (if running with multiple platforms simultaneously).

My current idea is to make the session id match up with the platform id. Then if I could grab the platform id in the test, I could create the correct webdriver client object.

Start by tracing the test server's per-browser WebDriver sessions and the TestPlatform API, since no files or tests are identified in the issue. Determine how a running test could receive its platform identifier and how that maps to the correct session; done means tests can reliably select the matching WebDriver client when multiple platforms run simultaneously.

Written by the indexing model from the issue text.