Make startSES aware of accessor properties.

* If a property is an accessor property, traverse the getter rather
  than invoking it and using its return value. This avoids possibly
  causing side-effects while traversing, and handles accessors on
  prototypes which throw if not called on an instance.
* Introduce a new whitelist value, 'accessor'; properties which
  are whitelisted as such but not actually accessors are rejected,
  as are properties which are accessors but whitelisted as data.
* Check syntax of whitelist as part of register().
* Shorten getThrowTypeError code by using 'gopd'.

@r5508

[kpreid_google, 2013-07-24 20:17:23]

Note on the motivation: This change is necessary to be able to whitelist
accessor properties. In ES5, there are no accessor properties on primordial
objects, but in ES6 there will be. Furthermore, Typed Arrays on Firefox already
use accessor properties on their prototypes; being able to use Typed Arrays from
guest code is the motivation for making this change.

[MarkM, 2013-07-24 22:39:14]

LGTM

https://codereview.appspot.com/11778043/diff/1/src/com/google/caja/ses/startS...
File src/com/google/caja/ses/startSES.js (right):

https://codereview.appspot.com/11778043/diff/1/src/com/google/caja/ses/startS...
src/com/google/caja/ses/startSES.js:1600: // Note this is safe not in that it is
safe for the prop to be an
Copy paste error? Inverted comment?

https://codereview.appspot.com/11778043/diff/1/src/com/google/caja/ses/whitel...
File src/com/google/caja/ses/whitelist.js (right):

https://codereview.appspot.com/11778043/diff/1/src/com/google/caja/ses/whitel...
src/com/google/caja/ses/whitelist.js:51: *     <p>If the property is an accessor
property, it is not
Do you really want a paragraph break within an <li> section?

[kpreid2, 2013-07-25 16:33:03]

@r5508

https://codereview.appspot.com/11778043/diff/1/src/com/google/caja/ses/startS...
File src/com/google/caja/ses/startSES.js (right):

https://codereview.appspot.com/11778043/diff/1/src/com/google/caja/ses/startS...
src/com/google/caja/ses/startSES.js:1600: // Note this is safe not in that it is
safe for the prop to be an
On 2013/07/24 22:39:14, MarkM wrote:
> Copy paste error? Inverted comment?

Copy-paste and also I neglected to revise the comment since an earlier version
(we _are_ cleaning).

https://codereview.appspot.com/11778043/diff/1/src/com/google/caja/ses/whitel...
File src/com/google/caja/ses/whitelist.js (right):

https://codereview.appspot.com/11778043/diff/1/src/com/google/caja/ses/whitel...
src/com/google/caja/ses/whitelist.js:51: *     <p>If the property is an accessor
property, it is not
On 2013/07/24 22:39:14, MarkM wrote:
> Do you really want a paragraph break within an <li> section?

Removed.

That is valid, but on second thought not a good idea in this way as it results
in inconsistent formatting; any given list should contain either all bare text
or all paragraphs, not a mix.