Fix Proxy invariant violations checked by Chrome.

* Both SES and ES5/3 proxy-based ArrayLikes now correctly report .length
  as configurable.
* <form> elements no longer return a list of property names containing
  'length' twice.
* Added toString methods to proxy handlers in ES5/3. (Unfortunately,
  they did not help in tracking down this bug due to
  <https://code.google.com/p/v8/issues/detail?id=2832>.)

Fixes <https://code.google.com/p/google-caja/issues/detail?id=1696>.

@r5538

[ihab.awad, 2013-08-07 21:46:53]

lgtm

https://codereview.appspot.com/12523045/diff/1/src/com/google/caja/plugin/dom...
File src/com/google/caja/plugin/domado.js (right):

https://codereview.appspot.com/12523045/diff/1/src/com/google/caja/plugin/dom...
src/com/google/caja/plugin/domado.js:5343: // here it would be a duplicate.
... because 'length' is non-enumerable?

[kpreid_google, 2013-08-07 21:48:17]

* Both SES and ES5/3 proxy-based ArrayLikes now correctly report .length
  as configurable.
* <form> elements no longer return a list of property names containing
  'length' twice.
* Added toString methods to proxy handlers in ES5/3. (Unfortunately,
  they did not help in tracking down this bug due to
  <https://code.google.com/p/v8/issues/detail?id=2832>.)

Fixes <https://code.google.com/p/google-caja/issues/detail?id=1696>.

[kpreid_google, 2013-08-07 21:48:21]

https://codereview.appspot.com/12523045/diff/1/src/com/google/caja/plugin/dom...
File src/com/google/caja/plugin/domado.js (right):

https://codereview.appspot.com/12523045/diff/1/src/com/google/caja/plugin/dom...
src/com/google/caja/plugin/domado.js:5343: // here it would be a duplicate.
On 2013/08/07 21:46:54, ihab.awad wrote:
> ... because 'length' is non-enumerable?

Done.

[MarkM, 2013-08-07 22:35:48]

ses/* parts LGTM