Summary:
1. Manually deleted #include "util/string_util.h" from util/testharness.h
2.
```
% USE_CLANG=1 make all -j55 -k 2> build.log
% perl -naF: -E 'say $F[0] if /: error:/' build.log | sort -u | xargs sed -i '/#include "util\/testharness.h"/i #include "util\/string_util.h"'
```

Test Plan:
Make sure make all completes with no errors.
```
% make all -j55
```

Reviewers: meyering, igor, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D35493