Why?
The fact that there's a MessageLoop on the thread is an
unnecessary implementation detail. When browser threads
are migrated to base/task_scheduler, tasks will no longer
have access to a MessageLoop.

These changes were generated manually.

Note: Some files outside of base/ had to be modified
because they didn't compile anymore after
#include "base/message_loop/message_loop.h" was removed
from base/ headers.

BUG=616447
TBR=rogerta@chromium.org

Review-Url: https://codereview.chromium.org/2136563002
Cr-Commit-Position: refs/heads/master@{#406378}