Remove MessageLoop{UI,IO}::{current,IsCurrent}()

This patch removes the deprecated
MessageLoop{UI,IO}::{current,IsCurrent} functions and rewrites clients
to MessageLoopCurrentFor{UI,IO}::{Current,IsSet}.

No functional changes.

# chrome/
TBR=sky@chromium.org
# extensions/
TBR=finnur@chromium.org
# net/
TBR=morlovich@chromium.org
# remoting/
TBR=garykac@chromium.org
# services/
TBR=rockot@google.com
# ui/
TBR=sadrul@chromium.org

Bug: 891670
Change-Id: I283cd67940e21e5b737d566a2ac351b69756e176
Reviewed-on: https://chromium-review.googlesource.com/c/1354010
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Reviewed-by: Gary Kacmarcik <garykac@chromium.org>
Reviewed-by: Joe Mason <joenotcharles@google.com>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612307}
42 files changed