Remove unused WebPrivatePtr::operator=(std::nullptr_t).

Remove unused WebPrivatePtr::operator=(std::nullptr_t).

With std::nullptr_t constructors in place for the various Ptr types,
this method is no longer needed.

Also revert some reset() uses that were introduced while waiting for
the same nullptr change to land.

R=abarth@chromium.org
BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=167612

[sof, 2014-02-21 11:47:50]

Please take a look.

With nullptr(_t) changes safely landed, following up on some WebPrivatePtr
details.

[abarth-chromium, 2014-02-21 17:37:24]

lgtm

[sof, 2014-02-21 17:40:27]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2014-02-21 17:40:42]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sigbjornf@opera.com/173713008/1

[commit-bot: I haz the power, 2014-02-21 18:23:43]

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

[commit-bot: I haz the power, 2014-02-21 18:23:43]

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 or
a lowly provisional 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.

[commit-bot: I haz the power, 2014-02-21 18:24:00]

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

[commit-bot: I haz the power, 2014-02-21 18:24:01]

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 or
a lowly provisional 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.

[sof, 2014-02-21 19:14:06]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2014-02-21 19:14:14]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sigbjornf@opera.com/173713008/1

[commit-bot: I haz the power, 2014-02-21 20:29:59]

Change committed as 167612