WIP: more performance view instrumentation.

Specifically in the case for no-one is listening.

We can be more aggressive yet, once we settle on some idea I can propagate it through ember.

We we had a global `instrumentingMode === true` we could easily fast path, all the instrumenting code. [like here](https://github.com/emberjs/ember.js/pull/5146/files#diff-162a95b4162d14de7e38fd4debc5fbd4R114)

Additionally, we should publish instrumentation hooks out-of-band [like here](https://github.com/tildeio/rsvp.js/blob/master/lib/rsvp/instrument.js#L7) this will prevent the cost of informing ember-extension and other tooling from effecting typical app usage. 

cc @krisselden