This was causing the renderer to sometimes grind to a halt with virtual time enabled.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fada7593e93c5a07ec3cbbb5cee01eaf78d421cf

commit fada7593e93c5a07ec3cbbb5cee01eaf78d421cf
Author: alexclarke <alexclarke@chromium.org>
Date: Wed Jul 27 12:09:03 2016

Fix TimeDomain::MigrateQueue with incoming immediate tasks

There's a bug with TimeDomain::MigrateQueue, it should add the TaskQueue
to the destination_time_domain's updatable_queue_set_ if the queue was
updatable.  Not doing so runs the risk of incoming tasks never running,
unless a subsequent immediate task is posted to the queue.

Note to Perf sheriffs.  I'm not expecting any regressions with
this patch, but it's possible some tasks that were previously
not running are running now.  If that causes a regression it's
working as intended.

BUG= 631941 ,  546953 

Review-Url: https://codereview.chromium.org/2189573002
Cr-Commit-Position: refs/heads/master@{#408098}

[modify] https://crrev.com/fada7593e93c5a07ec3cbbb5cee01eaf78d421cf/components/scheduler/base/task_queue_manager_unittest.cc
[modify] https://crrev.com/fada7593e93c5a07ec3cbbb5cee01eaf78d421cf/components/scheduler/base/time_domain.cc
[modify] https://crrev.com/fada7593e93c5a07ec3cbbb5cee01eaf78d421cf/components/scheduler/base/time_domain.h