Previously, DevTools filtered empty commits on the backend, while profiling, through the use of a bailout heuristic that React currently happens to use. This approach was brittle and may have exacerbated the long-standing Profiler bug #16446.
This PR removes that heuristic and adds as a post-processing filtering pass instead. This removes the coupling between DevTools and a React internal implementation detail that may change.
I believe DevTools has two choices of criteria for this filtering:
* Filter commits that have no actual duration metadata.
* Filter commits that have no recorded operations (no mutations to the tree, no changed tree base durations).
I chose the first option, filtering by commits that have no reported metadata. It will miss an edge case, e.g. , but we would have nothing meaningful to show in the Profiler for those cases anyway. (This particular edge case is why one of the snapshots changed with this commit.)
The second option, filtering by recorded operations, could potentially miss a more important edge case: where a component *did* render, but its didn't change. (In that event, there would be no operations to send.)
I used to disable the <- and -> buttons when you reached the beginning or end of the profiler data. This can be kind of annoying though when you just want to get to the last commit, and I don't think there's a good reason to enforce it anyway, so I backed that change out. The buttons now wrap around at the beginning or end of the list.
* Added anchor dom element in order to successfully download profiling data.
* Reworked downloadFile to accept a DOMElement in order for FF to successfully download profiling data.
* Prettify downloadFile changes.
