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This CL adds a some logic to read registry key values to control
the logging state for the host.  I've also integrated the
EventTraceData class with the EtwTraceConsumer for parsing.

The WXS file creates the logging reg key but by default we don't
log anything.  If logging is enabled, then we will create the
ETW classes to control and consume the events.  Once we have
ensured that the functionality is stable and have worked out any
issues, we can consider whether to turn it on by default.

The next CL will add the file logging and event logging classes.
I'd like to land this first to keep the CLs small and get as much
in before branch point as possible.

Bug: 1144185
Change-Id: I5778e57651b6afc99819140c911c2ace79803d74
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2535011Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826926}