Revert of scheduler: Always create a real scheduler in unit tests

Revert of scheduler: Always create a real scheduler in unit tests (patchset #10 id:180001 of https://codereview.chromium.org/1152623008/)

Reason for revert:
Caused crashes of webkit_unit_tests.
e.g. http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux/builds/48714

Original issue's description:
> scheduler: Always create a real scheduler in unit tests
>
> Previously we would create a dummy scheduler in any test which uses
> TestBlinkWebUnitTestSupport without first initializing a message loop.
> This causes problems because the dummy scheduler ignores all tasks it
> is given.
>
> This patch makes the tests more realistic by always creating a real
> renderer scheduler regardless of whether we have a message loop or not.
> This is achieved by lazily binding the scheduler to the message loop
> the first time it is needed.
>
> Longer term we would like to refactor these test suites to ensure Blink
> always has a valid message loop when it is initialized, but this will
> involve rewiring several tests.
>
> BUG=463143, 495659
>
> Committed: https://crrev.com/087644f1eab41927823a1a2fc2df08bd4e10fe18
> Cr-Commit-Position: refs/heads/master@{#332685}

TBR=rmcilroy@chromium.org,alexclarke@chromium.org,sievers@chromium.org,skyostil@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=463143, 495659
Committed: https://crrev.com/1c9dfd53fee588bdca753d2ccc1be7a47011afd1
Cr-Commit-Position: refs/heads/master@{#332758}

[tkent, 2015-06-04 01:27:28]

Created Revert of scheduler: Always create a real scheduler in unit tests

[commit-bot: I haz the power, 2015-06-04 01:28:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1156463004/1

[commit-bot: I haz the power, 2015-06-04 01:30:01]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-04 01:30:57]

Patchset 1 (id:??) landed as
https://crrev.com/1c9dfd53fee588bdca753d2ccc1be7a47011afd1
Cr-Commit-Position: refs/heads/master@{#332758}