Summary:
Add EventListener::OnTableFileCreated(), which will be called
when a table file is created.  This patch is part of the
EventLogger and EventListener integration.

Test Plan: Augment existing test in db/listener_test.cc

Reviewers: anthony, kradhakrishnan, rven, igor, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D38865