Fix content verifier problem with content scripts

Fix content verifier problem with content scripts

The problem is that we were creating the ContentVerifier too late
in ExtensionSystemImpl::Shared::Init, after the script loader had
already tried grabbing a reference to it for use on another
thead. Therefore at run time, for all content scripts we were was
seeing a null pointer for the content verifier and skipping
verification of those scripts.

BUG=509130
Committed: https://crrev.com/fe6dc62c549db502a0323ebbebab7ffd4f5cebd7
Cr-Commit-Position: refs/heads/master@{#339283}

[asargent_no_longer_on_chrome, 2015-07-13 18:19:50]

asargent@chromium.org changed reviewers:
+ rockot@chromium.org

[asargent_no_longer_on_chrome, 2015-07-13 21:01:54]

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

[commit-bot: I haz the power, 2015-07-13 21:03:07]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1226163010/40001

[commit-bot: I haz the power, 2015-07-13 23:29:22]

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

[commit-bot: I haz the power, 2015-07-13 23:29:23]

Dry run: This issue passed the CQ dry run.

[asargent_no_longer_on_chrome, 2015-07-16 19:35:53]

rockot: friendly ping

[Ken Rockot(use gerrit already), 2015-07-16 19:42:58]

lgtm

[asargent_no_longer_on_chrome, 2015-07-16 19:50:37]

The CQ bit was checked by asargent@chromium.org

[commit-bot: I haz the power, 2015-07-16 19:52:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1226163010/40001

[commit-bot: I haz the power, 2015-07-16 20:33:34]

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

[commit-bot: I haz the power, 2015-07-16 20:33:35]

Try jobs failed on following builders:
  linux_chromium_compile_dbg_32_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  mac_chromium_rel_ng on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

(exceeded global retry quota)

[asargent_no_longer_on_chrome, 2015-07-16 21:36:39]

The CQ bit was checked by asargent@chromium.org

[commit-bot: I haz the power, 2015-07-16 21:39:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1226163010/40001

[asargent_no_longer_on_chrome, 2015-07-16 21:46:38]

Patchset #4 (id:60001) has been deleted

[asargent_no_longer_on_chrome, 2015-07-17 17:25:49]

The CQ bit was checked by asargent@chromium.org

[commit-bot: I haz the power, 2015-07-17 17:26:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1226163010/40001

[commit-bot: I haz the power, 2015-07-17 18:10:28]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-07-17 18:11:17]

Patchset 3 (id:??) landed as
https://crrev.com/fe6dc62c549db502a0323ebbebab7ffd4f5cebd7
Cr-Commit-Position: refs/heads/master@{#339283}

[kelvinp, 2015-07-18 00:07:23]

A revert of this CL (patchset #3 id:40001) has been created in
https://codereview.chromium.org/1243533005/ by kelvinp@chromium.org.

The reason for reverting is: The ContentVerifierTest.ContentScripts test
introduced in this change has been failing 
consistently on Vista. See below

http://build.chromium.org/p/chromium.win/builders/Vista%20Tests%20%281%29/bui...
http://build.chromium.org/p/chromium.win/builders/Vista%20Tests%20%281%29/bui....