Bug 1448053 - be more efficient in MessageChannel::RepostAllMessages; r=jld

Once we've figured out that some task needs to be reposted, there's no
reason to continue scanning the list to find other tasks that need to be
reposted, since the logic in this function just requires one task that
needs to be reposted.

ipc/glue/MessageChannel.cpp

@@ -2855,6 +2855,7 @@ MessageChannel::RepostAllMessages()
     for (MessageTask* task : mPending) {
         if (!task->IsScheduled()) {
             needRepost = true;
+            break;
         }
     }
     if (!needRepost) {