Add HttpUrlConnection backed implementation of CronetEngine.

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

 // Copyright 2014 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.CronetEngine;
 
 import java.io.IOException;
 import java.net.Proxy;
@@ skipping 26 matching lines @@
     public URLConnection openConnection(URL url) throws IOException {
         return mCronetEngine.openConnection(url);
     }
 
     /**
      * Establishes a new connection to the resource specified by the {@link URL} {@code url}
      * using the given proxy.
      * @return an {@link java.net.HttpURLConnection} instance implemented by Cronet.
      */
     @Override
-    public URLConnection openConnection(URL url, Proxy proxy) {
+    public URLConnection openConnection(URL url, Proxy proxy) throws IOException {
         return mCronetEngine.openConnection(url, proxy);
     }
 }