Reland of Adding task runner/ message loop to tests that use IsolateHolder.

Reland of "Adding task runner/ message loop to tests that use IsolateHolder."

Reason for reland: Fixed mac build. Original CL: crrev.com/1130433002
For adding v8 heap memory dump provider, the gin::IsolateHolder needs
to have a task runner at initialization. The tests which don't
initiallize task runner when initialization are changed in this CL to
have either the message loop initializaed earlier or a dummy task
runner. Refer crrev.com/1088683003 for the dump provider.

BUG=476013
TBR=jochen@chromium.org,skyostil@chromium.org

Committed: https://crrev.com/93b23d9f113f01c0c19078bed47a47283dec0fbd
Cr-Commit-Position: refs/heads/master@{#328747}

[ssid, 2015-05-07 08:32:45]

Patchset #2 (id:20001) has been deleted

[ssid, 2015-05-07 08:32:51]

Patchset #2 (id:40001) has been deleted

[ssid, 2015-05-07 08:34:26]

ssid@chromium.org changed reviewers:
+ jochen@chromium.org, primiano@chromium.org, skyostil@chromium.org

[ssid, 2015-05-07 08:34:27]

PTAL.

[Primiano Tucci (use gerrit), 2015-05-07 08:37:05]

LGTM.
Given that this is a reland and the diff is one line change for which you just
got a review, it should be ok to TBR the previous reviewers and tick it ;-)

[ssid, 2015-05-07 08:45:23]

The CQ bit was checked by ssid@chromium.org

[commit-bot: I haz the power, 2015-05-07 08:45:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1129873002/60001

[commit-bot: I haz the power, 2015-05-07 10:33:46]

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

[commit-bot: I haz the power, 2015-05-07 10:33:49]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[ssid, 2015-05-07 12:07:25]

The CQ bit was checked by ssid@chromium.org

[commit-bot: I haz the power, 2015-05-07 12:07:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1129873002/60001

[commit-bot: I haz the power, 2015-05-07 12:11:17]

Committed patchset #2 (id:60001)

[commit-bot: I haz the power, 2015-05-07 12:12:17]

Patchset 2 (id:??) landed as
https://crrev.com/93b23d9f113f01c0c19078bed47a47283dec0fbd
Cr-Commit-Position: refs/heads/master@{#328747}