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This CL adds the class which consumes the ETW events from
Windows.  The class is fairly straight-forward but there
is one interesting bit as the call to consumer events
blocks us from running tasks on that thread.  In order to
receive events and not block any of the existing threads,
we create a new AutoThread which we use to listen for and
handle events on.  When it is time to clean up, we unblock
the listening thread by stopping the trace session.

Future CLs will add the logic needed to parse the events
and redirect the output to a new location (likely based on
registry settings).  I've kept that out of this CL to keep
its size on the smaller side.

Bug: 1144185
Change-Id: Iadfb2f73dc6f713face4117fc269bded85e182dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518087
Commit-Queue: Jamie Walch <jamiewalch@chromium.org>
Auto-Submit: Joe Downing <joedow@chromium.org>
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823740}