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This function binds a callback to a task runner. The functionality
already existed in media::BindToLoop() so it's intended to replace it
and is built on the same BindPostTaskTrampoline logic. BindToLoop() and
BindToCurrentLoop() will be replaced in a follow up CL since they are
used rather widely already.

There are some changes to the existing BindToLoop implementation:
1. Get the FROM_HERE location from the caller automatically rather than
   using the BindPostTask() location.
2. If BindPostTaskTrampoline has a OnceClosure, don't rebind the closure
   before posting a task.
3. Add static_assert to provide a readable error message explaining the
   input callback must have a void return type.
4. Don't support RepeatingCallback. This is more problematic since we
   will always PostTask() to destroy the callback. This is easier to add
   later than it would be to remove support.

Bug: 1140582
Change-Id: Ibb224b44c0b0c01dd88d29e94c7e9449d3353ef5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495055
Commit-Queue: kylechar <kylechar@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827818}