Cleanup after TF super.prop

Cleanup after  TF super.prop

Assign null when declaring to ensure no branch can ever keep the
value unassigned.

BUG=N
LOG=N
R=adamk@chromium.org, brucedawson@chromium.org

[arv (Not doing code reviews), 2015-06-08 17:58:49]

PTAL

[brucedawson, 2015-06-08 18:03:56]

lgtm. Thanks for addressing this.

The impetus for this, BTW, came from the /analyze builder. I check its results
every morning and it reported this new warning today:

src\v8\src\compiler\ast-graph-builder.cc(2270) : warning C6001: Using
uninitialized memory 'value'.

Setting up to check its results is somewhat cumbersome and low value so I don't
expect other people to being checking it.

[arv (Not doing code reviews), 2015-06-08 18:14:57]

The CQ bit was checked by arv@chromium.org

[commit-bot: I haz the power, 2015-06-08 18:15:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1151303008/1

[commit-bot: I haz the power, 2015-06-08 18:15:17]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-08 18:15:18]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[brucedawson, 2015-06-08 18:18:55]

I'm a full Chromium committer, but not a v8 committer.

[arv (Not doing code reviews), 2015-06-08 18:19:47]

arv@chromium.org changed reviewers:
+ adamk@chromium.org
- mstarzinger@chromium.org

[arv (Not doing code reviews), 2015-06-08 18:20:07]

Adam, care to take a quick look?

[arv (Not doing code reviews), 2015-06-08 18:23:10]

Closing in favor of https://codereview.chromium.org/1156293003/