Rework analysis server performance measurement code.

Rework analysis server performance measurement code.

This change has the following advantages:

- We now keep track of the amount of time spent doing unknown
  activities using its own timer.

- Several pieces of analysis server functionality are now tracked
  (previously we only tracked time spent inside the "analyzer"
  package).

- The set of all performance timers is tracked in PerformanceTag.all
  so that new timers can be added without having to update the code
  that prints out timing measurements.

- Performance measurement code has been integrated with Observatory
  "user tags", so that the same categories measured by the analysis
  server also show up in the VM profiler view.

R=brianwilkerson@google.com

Committed: https://code.google.com/p/dart/source/detail?r=43745

[Paul Berry, 2015-02-12 22:38:30]

paulberry@google.com changed reviewers:
+ brianwilkerson@google.com

[Brian Wilkerson, 2015-02-12 22:53:50]

LGTM

[Paul Berry, 2015-02-12 23:55:03]

Committed patchset #1 (id:1) manually as 43745 (presubmit successful).