Commits on Jul 16, 2015

1. Wire up the JS engine's memory reporting. …

   SpiderMonkey provides an extremely fine-grained breakdown of memory
   usage, but for Servo we aggregate the measurements into a small number
   of coarse buckets, which seems appropriate for the current level of
   detail provided by Servo's memory profiler. Sample output:
   ```
   |   10.99 MiB -- pages
   |       7.75 MiB -- url(http://html5demos.com/worker)
   |          4.63 MiB -- js
   |             2.00 MiB -- gc-heap
   |                0.94 MiB -- decommitted
   |                0.92 MiB -- used
   |                0.09 MiB -- unused
   |                0.05 MiB -- admin
   |             1.44 MiB -- malloc-heap
   |             1.19 MiB -- non-heap
   |          [...]
   |       3.24 MiB -- url(http://html5demos.com/js/worker-cruncher.js)
   |          3.24 MiB -- js
   |             1.17 MiB -- malloc-heap
   |             1.06 MiB -- non-heap
   |             1.00 MiB -- gc-heap
   |                0.69 MiB -- used
   |                0.19 MiB -- decommitted
   |                0.09 MiB -- unused
   |                0.03 MiB -- admin
   ```
   Most of the changes are plumbing to get the script and worker tasks
   communicating with the memory profiler task.

   

   nnethercote committed Jul 16, 2015

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