Add DCHECK that the script context table do not contain native scripts.

Add DCHECK that the script context table do not contain native scripts.

This is to prevent unnecessary script contexts to be created for
native scripts, which could end up with a script context table
containing twenty script contexts for a newly created native context.

R=jkummerow@chromium.org

Committed: https://crrev.com/f0c21aa487cfab274f21a12c5f64af4b690f1b32
Cr-Commit-Position: refs/heads/master@{#30188}

[Jakob Kummerow, 2015-08-17 09:37:27]

lgtm

[Yang, 2015-08-17 09:58:28]

The CQ bit was checked by yangguo@chromium.org

[commit-bot: I haz the power, 2015-08-17 09:58:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1301533002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1301533002/1

[commit-bot: I haz the power, 2015-08-17 11:00:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-17 11:01:04]

Patchset 1 (id:??) landed as
https://crrev.com/f0c21aa487cfab274f21a12c5f64af4b690f1b32
Cr-Commit-Position: refs/heads/master@{#30188}