DevTools: add tests to fixate bindings behavior

This patch adds a bunch of tests to fixate bindings behavior:
- bindings-* tests ensure that workspace is populated correctly
- navigator-* tests ensure that navigator is populated correctly

The binding-* and navigator-* tests are very similar, but since
navigator might rely less on workspace in future, they're kept separate.

These tests will help to evaluate changes which will happen to bindings
and navigator during bindings refactoring.

BUG=670180
R=dgozman

Review-Url: https://codereview.chromium.org/2735933002
Cr-Commit-Position: refs/heads/master@{#455531}