[debugger] Add test for Debug.scripts without listener.

[debugger] Add test for Debug.scripts without listener.

This adds a test case that ensures calling Debug.scripts without any
listener attached fails gracefully. For now we are throwing the string
"illegal access", this might change in the future to be a dedicated
exception.

R=yangguo@chromium.org
TEST=mjsunit/debug-scripts-throw

Committed: https://crrev.com/169627564215dcdedd1c5fb308b73e2a2a512339
Cr-Commit-Position: refs/heads/master@{#31377}

[Michael Starzinger, 2015-10-19 09:49:54]

mstarzinger@chromium.org changed reviewers:
+ info@bnoordhuis.nl

[Michael Starzinger, 2015-10-19 09:49:55]

Yang: PTAL.
Ben: FYI.

[Yang, 2015-10-19 10:18:50]

On 2015/10/19 09:49:55, Michael Starzinger wrote:
> Yang: PTAL.
> Ben: FYI.

LGTM.

[Michael Starzinger, 2015-10-19 13:32:55]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-10-19 13:32:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1411193002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1411193002/1

[commit-bot: I haz the power, 2015-10-19 13:34:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-19 13:34:50]

Patchset 1 (id:??) landed as
https://crrev.com/169627564215dcdedd1c5fb308b73e2a2a512339
Cr-Commit-Position: refs/heads/master@{#31377}