Remove use of WebTaskRunner::Task and SameThreadTask from Microtask

Remove use of WebTaskRunner::Task and SameThreadTask from Microtask

Microtask uses WebTaskRunner::Task and SameThreadTask, but it is not necessary
after the last use of
Microtask::enqueueMicrotask(std::unique_ptr<WebTaskRunner::Task>) was removed
by https://codereview.chromium.org/1976083002/.

This CL makes Microtask to use SameThreadClosure directly.

BUG=478194
Committed: https://crrev.com/272c48dea84453021a475c33bf1223173f645be4
Cr-Commit-Position: refs/heads/master@{#394014}

[hiroshige, 2016-05-13 07:41:12]

The CQ bit was checked by hiroshige@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-05-13 07:41:30]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1978583003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1978583003/1

[hiroshige, 2016-05-13 08:00:13]

hiroshige@chromium.org changed reviewers:
+ haraken@chromium.org

[hiroshige, 2016-05-13 08:00:14]

PTAL.

[haraken, 2016-05-13 08:01:02]

LGTM

[commit-bot: I haz the power, 2016-05-13 09:11:51]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-05-13 09:11:51]

Dry run: This issue passed the CQ dry run.

[hiroshige, 2016-05-17 00:10:03]

The CQ bit was checked by hiroshige@chromium.org

[commit-bot: I haz the power, 2016-05-17 00:10:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1978583003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1978583003/1

[commit-bot: I haz the power, 2016-05-17 01:49:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-05-17 01:50:23]

Description was changed from

==========
Remove use of WebTaskRunner::Task and SameThreadTask from Microtask

Microtask uses WebTaskRunner::Task and SameThreadTask, but it is not necessary
after the last use of
Microtask::enqueueMicrotask(std::unique_ptr<WebTaskRunner::Task>) was removed
by https://codereview.chromium.org/1976083002/.

This CL makes Microtask to use SameThreadClosure directly.

BUG=478194
==========

to

==========
Remove use of WebTaskRunner::Task and SameThreadTask from Microtask

Microtask uses WebTaskRunner::Task and SameThreadTask, but it is not necessary
after the last use of
Microtask::enqueueMicrotask(std::unique_ptr<WebTaskRunner::Task>) was removed
by https://codereview.chromium.org/1976083002/.

This CL makes Microtask to use SameThreadClosure directly.

BUG=478194

Committed: https://crrev.com/272c48dea84453021a475c33bf1223173f645be4
Cr-Commit-Position: refs/heads/master@{#394014}
==========

[commit-bot: I haz the power, 2016-05-17 01:50:24]

Patchset 1 (id:??) landed as
https://crrev.com/272c48dea84453021a475c33bf1223173f645be4
Cr-Commit-Position: refs/heads/master@{#394014}