Revert parallel render patch due to issue #2718.
Update wpt
Merge pull request #2721 from Manishearth/wpt_up

Update web platform tests
Merge pull request #2719 from glennw/revert-parallel

Revert parallel render patch due to issue #2718.
Add a basic memory profiler, invoked with -m.
Rename |Profiler| as |TimeProfiler|.

And likewise for |ProfilerChan|, |profiler_chan|, and so on.  This
contrasts nicely with the newly added |MemoryProfiler|.