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I noticed today that the file logger in Windows still wrote a file
after I disabled it via the registry.  I tracked the issue down and
it's because the current impl starts the file/event log loggers if
the registry key exists (instead of checking for existence and then
checking the value).

This CL fixes that by only creating the logger instance if the
pertinent reg key exists and has a non-zero value.

Change-Id: I2dabd7c52af831af228fbc2217ced7fd14126ae1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2582425
Auto-Submit: Joe Downing <joedow@chromium.org>
Commit-Queue: Joe Downing <joedow@chromium.org>
Commit-Queue: Jamie Walch <jamiewalch@chromium.org>
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835335}