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This change introduces the SessionLogManager class. The
SessionLogManager owns the various logging classes and will be
responsible for constructing the session log when requested by the user.

Bug: 1128204
Change-Id: I4c41effce7d1faf99f2c68c773642e44aec18dfe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2632870
Commit-Queue: Bailey Berro <baileyberro@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844967}