bindings: Supports [LenientThis] extended attributes.

bindings: Supports [LenientThis] extended attributes.

When we moved DOM attributes to the prototype chain, we changed the type
of JS properties corresponding to the attributes to have get and set
(i.e. accessor type).  The change itself is correct, but it revealed that
we don't support [LenientThis] and Blink started throwing TypeError when
|this| is not a correct instance.

In order to keep backward compatibility, this CL supports [LenientThis]
extended attribute, and ignores type error for the following attributes.
- GlobalEventHandlers
  - onmouseenter
  - onmouseleave
- Document
  - onreadystatechange

BUG=472260
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=196551

[Yuki, 2015-06-04 10:38:17]

yukishiino@chromium.org changed reviewers:
+ bashi@chromium.org, haraken@chromium.org

[Yuki, 2015-06-04 10:38:17]

Could you guys review this CL?

[haraken, 2015-06-04 10:42:40]

The change looks good. Can we add a layout test?

[Yuki, 2015-06-04 14:08:19]

On 2015/06/04 10:42:40, haraken wrote:
> The change looks good. Can we add a layout test?

Yes, added.  Also I needed to fix the CL to take account of info.This().

[haraken, 2015-06-04 14:39:28]

LGTM

[bashi, 2015-06-05 00:17:17]

LGTM

[Yuki, 2015-06-05 04:00:13]

The CQ bit was checked by yukishiino@chromium.org

[commit-bot: I haz the power, 2015-06-05 04:00:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1161463009/40001

[commit-bot: I haz the power, 2015-06-05 04:04:37]

Committed patchset #3 (id:40001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=196551