Add some changes to TraceAnalyzer to improve analysis

* Tests which rely on being able to query for the end event in a pair
  were not possible, partly because end events tend to be missing
  information, and also because they did not reference their start
* Async event association can optionally be allowed for events which
  span across process boundaries


Cr-Commit-Position: refs/heads/master@{#455132}
(cherry picked from commit 83621ef58f633413145bd7093f16d56eb2c88103)
3 files changed