Cleaning up a little technical debt by adding docstrings
for our public APIs.
Note: I plan to submit a patch per file as part of this bug work.
These patches won't depend on each other. The last patch of
the series will close the bug.
Change-Id: I1490e6b69e62617d3d29bd9e0eb8eb0f76ab5cc6
Partial-Bug: #1614594
5cbb6f7731