ChannelOutboundBuffer returns total pending write size

total pending write size may be used to optimize write batching

transport/src/main/java/io/netty/channel/ChannelOutboundBuffer.java

@@ -545,6 +545,10 @@ public final class ChannelOutboundBuffer {
         RECYCLER.recycle(this, handle);
     }
 
+    public long totalPendingWriteBytes() {
+        return this.totalPendingSize;
+    }
+
     private static final class Entry {
         Object msg;
         ByteBuffer[] buffers;