DevTools: speculative fix of crash in PageDebuggerAgent::restore

DevTools: speculative fix of crash in PageDebuggerAgent::restore

It may happen that we navigate to a page where script execution is blocked. Debugger should not be anabled for such pages. This CL makes sure that we won't be restoring debugger state if we know for sure that the script execution is blocked.

restore() is called very early before the load starts hence at that point we don't know if the new page is blacklisted. This use case is not covered by this change and I'm hesitent complicating debugger code for such rare scenario.

BUG=498963
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=196937

[yurys, 2015-06-11 10:12:15]

yurys@chromium.org changed reviewers:
+ kozyatinskiy@chromium.org, sergeyv@chromium.org

[yurys, 2015-06-11 10:12:22]

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

[commit-bot: I haz the power, 2015-06-11 10:12:32]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1180713005/1

[sergeyv, 2015-06-11 10:34:10]

lgtm

[yurys, 2015-06-11 10:34:15]

The CQ bit was unchecked by yurys@chromium.org

[yurys, 2015-06-11 10:58:41]

The CQ bit was checked by yurys@chromium.org

[commit-bot: I haz the power, 2015-06-11 10:58:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1180713005/1

[commit-bot: I haz the power, 2015-06-11 11:26:09]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=196937