Remove knowledge of extensions from TabRestoreServiceHelper

Remove knowledge of extensions from TabRestoreServiceHelper

This CL removes the last problematic //chrome-level dependency from core
TabRestore code by abstracting TabRestoreServiceHelper's knowledge of the
extensions TabHelper through TabRestoreServiceClient.

BUG=371476
Committed: https://crrev.com/b5336a575fb216e06aebc70b2675737b67baf5a2
Cr-Commit-Position: refs/heads/master@{#348842}

[blundell, 2015-09-14 15:38:39]

blundell@chromium.org changed reviewers:
+ sky@chromium.org

[blundell, 2015-09-14 15:38:39]

Hi Scott,

This is dependent on https://codereview.chromium.org/1342743002/, so please look
at that one first. Thanks!

[sky, 2015-09-14 18:15:34]

LGTM

[blundell, 2015-09-15 05:49:58]

The CQ bit was checked by blundell@chromium.org

[blundell, 2015-09-15 05:49:58]

The patchset sent to the CQ was uploaded after l-g-t-m from sky@chromium.org
Link to the patchset: https://codereview.chromium.org/1345453002/#ps20001
(title: "Rebase")

[commit-bot: I haz the power, 2015-09-15 05:50:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1345453002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1345453002/20001

[commit-bot: I haz the power, 2015-09-15 06:41:58]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-09-15 06:42:37]

Patchset 2 (id:??) landed as
https://crrev.com/b5336a575fb216e06aebc70b2675737b67baf5a2
Cr-Commit-Position: refs/heads/master@{#348842}

[commit-bot: I haz the power, 2015-09-23 12:42:59]

Patchset 2 (id:??) landed as
https://crrev.com/b5336a575fb216e06aebc70b2675737b67baf5a2
Cr-Commit-Position: refs/heads/master@{#348842}