SpeedscopeRenderer: add test_profiler test
SpeedscopeRenderer: add test_profiler test

This commit adds a test to test_profiler that tests the JSON output
emitted by SpeedscopeRenderer against known properties it should have.

joerick/pyinstrument,joerick/pyinstrument,joerick/pyinstrument,joerick/pyinstrument,joerick/pyinstrument,joerick/pyinstrument