Bug 1470965: Fix refcount sanity in nsIPrincipal.addonPolicy getter. r=mixedpuppy

MozReview-Commit-ID: KuDN3joKi7S

--HG--
extra : rebase_source : e2caed633f39896df6c065abcb18791b582d8f59

caps/BasePrincipal.cpp

@@ -336,7 +336,8 @@ BasePrincipal::GetIsInIsolatedMozBrowserElement(bool* aIsInIsolatedMozBrowserEle
 nsresult
 BasePrincipal::GetAddonPolicy(nsISupports** aResult)
 {
-  *aResult = AddonPolicy();
+  RefPtr<extensions::WebExtensionPolicy> policy(AddonPolicy());
+  policy.forget(aResult);
   return NS_OK;
 }