Stop using namespace std.

The pattern of #include and using namespace std here fails to build
with GCC. At first glance it's a GCC bug rather than libc++ doing
something wrong. Regardless, it can be worked around by just
specifying std:: where appropriate.

Bug: 19606303
Change-Id: I5652682eae7ca7559cf2a9307909859013440781
3 files changed