Add missing <cassert> include

Previous versions of libc++ incidentally included <cassert> (assert.h)
via the <memory> header, but this was fixed:

https://reviews.llvm.org/rGa0686015106c2a04e85af82a4687895e12a4531c

Bug: none
Test: treehugger
Change-Id: I63bbdcdd45c93b94334cb798aa79933eddea01dc
2 files changed