Revert of Remove unused sourceData variable in InspectorStyleSheet.

Revert of Remove unused sourceData variable in InspectorStyleSheet. (patchset #1 id:1 of https://codereview.chromium.org/574963002/)

Reason for revert:
This code is still needed

Original issue's description:
> Remove unused sourceData variable in InspectorStyleSheet.
> 
> Breaks build for targets that treat unused variables as errors.
> 
> R=dgozman@chromium.org, vsevik@chromium.org
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=182145

TBR=dgozman@chromium.org,ager@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=182928

[vsevik, 2014-09-30 12:18:17]

Created Revert of Remove unused sourceData variable in InspectorStyleSheet.

[vsevik, 2014-09-30 12:21:42]

The CQ bit was checked by vsevik@chromium.org

[commit-bot: I haz the power, 2014-09-30 12:22:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/611333002/40001

[commit-bot: I haz the power, 2014-09-30 12:33:07]

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

[commit-bot: I haz the power, 2014-09-30 12:33:08]

Try jobs failed on following builders:
  mac_blink_compile_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_compile_dbg/bu...)

[vsevik, 2014-09-30 12:40:08]

The CQ bit was checked by vsevik@chromium.org

[commit-bot: I haz the power, 2014-09-30 12:41:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/611333002/60001

[commit-bot: I haz the power, 2014-09-30 14:25:43]

Committed patchset #3 (id:60001) as 182928