bug 1549249 - build bustage follow-up r=mt,dveditz a=tomprince

SECItem uses an unsigned int to indicate its length. We need to cast a size_t
down to the appropriate size. This is safe because what we're casting will
always fit in an unsigned int on the platforms we're using (it's just the size
of the intermediate certificate we added).

Differential Revision: https://phabricator.services.mozilla.com/D30144

--HG--
extra : source : 24bb6566385fc566f1a6b98ea24cad7d0af7e3a3

security/apps/AppTrustDomain.cpp

@@ -134,7 +134,8 @@ nsresult AppTrustDomain::SetTrustedRoot(AppTrustedRoot trustedRoot) {
     SECItem intermediateDER = {
         siBuffer,
         const_cast<uint8_t*>(addonsPublicIntermediate),
-        mozilla::ArrayLength(addonsPublicIntermediate),
+        static_cast<unsigned int>(
+            mozilla::ArrayLength(addonsPublicIntermediate)),
     };
     mAddonsIntermediate.reset(CERT_NewTempCertificate(
         CERT_GetDefaultCertDB(), &intermediateDER, nullptr, false, true));