[ES6 modules] Update module script error state predicate and transition.

This CL updates the following spec concepts:
"#concept-module-script-is-errored"
- Null record is now also treated as an error
"#concept-module-script-pre-instantiation-error"
- Renamed from module script's error.
"#concept-module-script-module-record"
- Implement "set its [[HostDefined]] field to undefined" step.
"#concept-module-script-set-pre-instantiation-error"
- Don't set script's state to errored.

This change is to be introduced in whatwg html spec PR:
https://github.com/whatwg/html/pull/2674

The actual implementation behavior change will be introduced in separate CLs.

Bug: 594639, 727299, https://github.com/whatwg/html/pull/2674
Change-Id: Ie9734344030f99bcdaa3d595f8dbec87d44a7c92
Reviewed-on: https://chromium-review.googlesource.com/541097
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#482213}
13 files changed