Create TaskScheduler for all Mojo apps.

Running mustash on device currently crashes on startup. This is because
ui::Service doesn't create a TaskScheduler before Ozone DRM uses it. One
option is to have ui::Service::OnStart() create a TaskScheduler. If
other Mojo applications need a task scheduler they'll have to do the
same. Instead, have MashRunner start a TaskRunner for each process.

This fixes the crash in Ozone DRM and doesn't seem to cause any other
problems.

BUG=679840

Review-Url: https://codereview.chromium.org/2621153003
Cr-Commit-Position: refs/heads/master@{#442956}
1 file changed