Deprecate MessageLoop::Type

It is currently just an alias to MessagePump::Type. This patch changes
a bunch of references to use MessagePump::Type as MessageLoop will eventually
disappear.

Also rename base::Thread::Options::message_loop_type to message_pump_type
It is weird to see things like

message_loop_type = MessagePump::Type::UI

Also change some other instances that I happened to see in the form
loop_type = MessagePump::Type::UI
to
pump_type = MessagePump::Type::UI

This is a mechanical change that will be reviewed according to
https://chromium.googlesource.com/chromium/src/+/master/docs/code_reviews.md#mechanical-changes

BUG=891670
[email protected]

Change-Id: Ib41ccc6547b8c9fa0bdba5d23c4767ae03f2a97d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1718331
Commit-Queue: Carlos Caballero <[email protected]>
Reviewed-by: Gabriel Charette <[email protected]>
Cr-Commit-Position: refs/heads/master@{#682254}
157 files changed