Don't call SetProperty on the plugin unless HasProperty is true

Don't call SetProperty on the plugin unless HasProperty is true

The default implementation of SetProperty in the plugin (inside
ScriptableObject) will throw an exception. This can result in an
unexpected exception in JS when properties are set on the plugin
element. We should only call SetProperty if the plugin has that
property.

BUG=414842
TBR=dmichael@chromium.org

Committed: https://crrev.com/0b40913d6e0cff095e373ea216680870d1215336
Cr-Commit-Position: refs/heads/master@{#299040}

[raymes, 2014-10-10 00:42:25]

raymes@chromium.org changed reviewers:
+ sammc@chromium.org

[Sam McNally, 2014-10-10 00:57:04]

lgtm

[raymes, 2014-10-10 00:58:29]

The CQ bit was checked by raymes@chromium.org

[commit-bot: I haz the power, 2014-10-10 00:59:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/640033003/30001

[commit-bot: I haz the power, 2014-10-10 02:05:44]

Committed patchset #2 (id:30001)

[commit-bot: I haz the power, 2014-10-10 02:06:22]

Patchset 2 (id:??) landed as
https://crrev.com/0b40913d6e0cff095e373ea216680870d1215336
Cr-Commit-Position: refs/heads/master@{#299040}

[dmichael (off chromium), 2014-10-10 15:40:02]

lgtm