Implement testing baseline

Observations from https://github.com/auchenberg/vscode-browser-preview/issues/122

There is a test but it doesn't look to be in use. I can't quite figure out what it does.

I want to have at least 3 sanity tests.

One that tests that the extension can be launched from vscode. I have no idea how to do this.
One that drives the current stable chrome and current chrome canary and verifies we can get a screencast and inspect a node.
One that tests that the UI shows up.

Start by locating the existing test mentioned in the issue and determine why it is not in use. Define the baseline around launching the extension from VS Code, exercising stable Chrome and Chrome Canary for screencast and node inspection, and verifying that the UI appears; done means all three sanity tests run and pass.

Written by the indexing model from the issue text.