[mojo] Introduce GenericPendingReceiver

This adds the GenericPendingReceiver type to the bindings library.
The type encapsulates a receiving pipe endpoint, paired with the name of
the interface assumed by the corresponding remote endpoint. This can be
used for convenience in place of an ad hoc string/pipe pair.

Bug: 977637
Change-Id: I8ff968e4f0d64c1beca1246f8b2dee3d2f3719db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674252
Reviewed-by: Oksana Zhuravlova <oksamyt@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#672193}
13 files changed