dbus: Update comment of ObjectProxy::WaitForServiceToBeAvailable

It is important to make clear that callbacks are executed in which
thread.

As ObjectProxy::RunWaitForServiceToBeAvailableCallbacks() asserts at its
first line, WaitForServiceToBeAvailableCallback are called in the origin
thread.

Bug: none
Change-Id: I8e90254edc75040f08ecca48c3227e82ff26f1b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5340776
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Shin Kawamura <kawasin@google.com>
Cr-Commit-Position: refs/heads/main@{#1268883}
NOKEYCHECK=True
GitOrigin-RevId: 1d3f42a27d83347245fcf8e2f150ff55ccce77da
1 file changed