Summary:
Google C++ Style writes: In particular, prefer to write lambda captures explicitly when capturing this or if the lambda will escape the current scope.
Here it is the case for both.

Test Plan: Run all test suites.

Reviewers: andrewkr, dhruba

Reviewed By: andrewkr, dhruba

Subscribers: yhchiang, IslamAbdelRahman, leveldb, andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D58515