Restore derived buffer index/mark updates

Motivation:
As part of the revert process in https://github.com/netty/netty/pull/4138 some index and mark updates were lost.

Modifications:
- Restore the index / mark updates made in https://github.com/netty/netty/pull/3788

Result:
Slice and Duplicate buffers index / marks are correctly initialized.

buffer/src/main/java/io/netty/buffer/DuplicatedByteBuf.java

@@ -45,6 +45,8 @@ public class DuplicatedByteBuf extends AbstractDerivedByteBuf {
         }
 
         setIndex(buffer.readerIndex(), buffer.writerIndex());
+        markReaderIndex();
+        markWriterIndex();
     }
 
     @Override

buffer/src/test/java/io/netty/buffer/DuplicateByteBufTest.java

@@ -17,7 +17,7 @@ package io.netty.buffer;
 
 import org.junit.Test;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
 
 /**
  * Tests duplicated channel buffers
@@ -28,8 +28,10 @@ public class DuplicateByteBufTest extends AbstractByteBufTest {
 
     @Override
     protected ByteBuf newBuffer(int length) {
-        buffer = new DuplicatedByteBuf(Unpooled.buffer(length));
-        assertEquals(0, buffer.writerIndex());
+        ByteBuf wrapped = Unpooled.buffer(length);
+        buffer = new DuplicatedByteBuf(wrapped);
+        assertEquals(wrapped.writerIndex(), buffer.writerIndex());
+        assertEquals(wrapped.readerIndex(), buffer.readerIndex());
         return buffer;
     }
 
@@ -54,4 +56,26 @@ public class DuplicateByteBufTest extends AbstractByteBufTest {
 
         assertEquals((byte) 0, buffer.readByte());
     }
+
+    @Test
+    public void testMarksInitialized() {
+        ByteBuf wrapped = Unpooled.buffer(8);
+        try {
+            wrapped.writerIndex(6);
+            wrapped.readerIndex(1);
+            ByteBuf duplicate = new DuplicatedByteBuf(wrapped);
+
+            // Test writer mark
+            duplicate.writerIndex(duplicate.writerIndex() + 1);
+            duplicate.resetWriterIndex();
+            assertEquals(wrapped.writerIndex(), duplicate.writerIndex());
+
+            // Test reader mark
+            duplicate.readerIndex(duplicate.readerIndex() + 1);
+            duplicate.resetReaderIndex();
+            assertEquals(wrapped.readerIndex(), duplicate.readerIndex());
+        } finally {
+            wrapped.release();
+        }
+    }
 }

buffer/src/test/java/io/netty/buffer/SlicedByteBufTest.java

@@ -20,7 +20,7 @@ import org.junit.Test;
 import java.io.IOException;
 import java.util.Random;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
 
 /**
  * Tests sliced channel buffers
@@ -113,4 +113,28 @@ public class SlicedByteBufTest extends AbstractByteBufTest {
     public void testLittleEndianWithExpand() {
        // ignore for SlicedByteBuf
     }
+
+    @Test
+    public void testReaderIndexAndMarks() {
+        ByteBuf wrapped = Unpooled.buffer(16);
+        try {
+            wrapped.writerIndex(14);
+            wrapped.readerIndex(2);
+            wrapped.markWriterIndex();
+            wrapped.markReaderIndex();
+            ByteBuf slice = new SlicedByteBuf(wrapped, 4, 4);
+            assertEquals(0, slice.readerIndex());
+            assertEquals(4, slice.writerIndex());
+
+            slice.readerIndex(slice.readerIndex() + 1);
+            slice.resetReaderIndex();
+            assertEquals(0, slice.readerIndex());
+
+            slice.writerIndex(slice.writerIndex() - 1);
+            slice.resetWriterIndex();
+            assertEquals(0, slice.writerIndex());
+        } finally {
+            wrapped.release();
+        }
+    }
 }