Don't rely on implicit lookup of member names in dependent base classes
Summary:
The standard says this shouldn't be done, but GCC, Clang, and MSVC all do, at least, MSVC does if you don't pass the `/permissive-` switch to disable this non-compliant lookup.
This just qualifies it with `this->` which solves the problem.
MSVC plans to eventually (some time after the 2017 release) enable `/permissive-` by default, so let's start compiling with it now.
Reviewed By: yfeldblum
Differential Revision:
D4200725
fbshipit-source-id:
8545c6bcda9ba6006733c15f668805cb1260517a