Tracing: stop() should return Promise<Buffer>

[ebidel]

It would be convenient if page.tracing.stop() returned Promise<Buffer> so users could act ton the trace JSON without saving a file to disk. This would also be consistent with the screenshot API.

[JoelEinbinder]

Pull requests welcome 😄

[ebidel]

Ping.

[kblok]

@ebidel, @aslushnikov I know I'm quite late here 😜but, Why would it need to return a buffer instead of just a simple string? We are building a buffer based on a string. Why not just returning that string to the client?

[aslushnikov]

@kblok iirc buffers are allowed to allocate more memory then strings.