Currently it purports to return nsresult, but always returns NS_OK. This is a type error in _setvalue() in nsNPAPIPlugin.cpp, since it ostensibly returns NPError but in one place returns the result of SetCached(). So let's just make it officially infallible so it's not an issue.
Created attachment 651704 [details] [diff] [review]
(This is the only caller.)
Green try: https://tbpl.mozilla.org/?tree=Try&rev=da4047717ef7
Sorry, correct revision link: https://hg.mozilla.org/integration/mozilla-inbound/rev/66ae8a550cfc