[Cronet] Change interface APIs to abstract classes

components/cronet/android/java/src/org/chromium/net/urlconnection/CronetOutputStream.java

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.net.urlconnection;
 
 import org.chromium.net.UploadDataProvider;
 
 import java.io.IOException;
 import java.io.OutputStream;
 
 /**
  * An abstract class of {@link OutputStream} that concrete implementations must
  * extend in order to be used in {@link CronetHttpURLConnection}.
  */
-abstract class CronetOutputStream extends OutputStream implements UploadDataProvider {
+abstract class CronetOutputStream extends OutputStream {
     /**
      * Tells the underlying implementation that connection has been established.
      * Used in {@link CronetHttpURLConnection}.
      */
     abstract void setConnected() throws IOException;
 
     /**
      * Checks whether content received is less than Content-Length.
      * Used in {@link CronetHttpURLConnection}.
      */
     abstract void checkReceivedEnoughContent() throws IOException;
+
+    /**
+     * Returns {@link UploadDataProvider} implementation.
+     */
+    abstract UploadDataProvider getUploadDataProvider();
 }