Update docs for InterfacePtr and Binding.

Bug: None
Change-Id: I476e1ba191391085cc6719b07c90fa0a6f2e42db
Reviewed-on: https://chromium-review.googlesource.com/775676
Reviewed-by: James Cook <[email protected]>
Cr-Commit-Position: refs/heads/master@{#517210}
3 files changed