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
TBR=gab@chromium.org

Change-Id: Ib41ccc6547b8c9fa0bdba5d23c4767ae03f2a97d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1718331
Commit-Queue: Carlos Caballero <carlscab@google.com>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682254}

diff --git a/chromeos/process_proxy/process_output_watcher_unittest.cc b/chromeos/process_proxy/process_output_watcher_unittest.cc
index 969cc60..e58c36f 100644
--- a/chromeos/process_proxy/process_output_watcher_unittest.cc
+++ b/chromeos/process_proxy/process_output_watcher_unittest.cc

@@ -16,6 +16,7 @@
 #include "base/callback.h"
 #include "base/files/file_util.h"
 #include "base/location.h"
+#include "base/message_loop/message_pump_type.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
@@ -146,7 +147,7 @@
     ASSERT_FALSE(output_watch_thread_started_);
     output_watch_thread_.reset(new base::Thread("ProcessOutpuWatchThread"));
     output_watch_thread_started_ = output_watch_thread_->StartWithOptions(
-        base::Thread::Options(base::MessageLoop::TYPE_IO, 0));
+        base::Thread::Options(base::MessagePumpType::IO, 0));
     ASSERT_TRUE(output_watch_thread_started_);
 
     int pt_pipe[2];