[base] Implement std::size(), std::empty() and std::data()

This change provides C++14 implementations of C++17's std::size(),
std::empty() and std::data().

Bug: 828324
Change-Id: If1b83826a23b26fd557f7854962bcbc771a7ffe0
Reviewed-on: https://chromium-review.googlesource.com/992236
Commit-Queue: Jan Wilken Dörrie <[email protected]>
Reviewed-by: kylechar <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Cr-Commit-Position: refs/heads/master@{#550137}

• base/stl_util.h[diff]
• base/stl_util_unittest.cc[diff]