[Cronet] Add API to set DNS cache entry

components/cronet/android/api/src/org/chromium/net/ExperimentalCronetEngine.java

 // Copyright 2016 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;
 
 import android.content.Context;
 import android.support.annotation.VisibleForTesting;
 
 import java.io.IOException;
+import java.net.InetAddress;
 import java.net.Proxy;
 import java.net.URL;
 import java.net.URLConnection;
 import java.util.Date;
 import java.util.Set;
 import java.util.concurrent.Executor;
 
 /**
  * {@link CronetEngine} that exposes experimental features. To obtain an
  * instance of this class, cast a {@code CronetEngine} to this type. Every
@@ skipping 407 matching lines @@
      * computed by the network quality estimator. Set to
      * {@link #CONNECTION_METRIC_UNKNOWN} if the value is
      * unavailable. This must be called after
      * {@link Builder#enableNetworkQualityEstimator}, and will
      * throw an exception otherwise.
      * @return Estimate of the downstream throughput in kilobits per second.
      */
     public int getDownstreamThroughputKbps() {
         return CONNECTION_METRIC_UNKNOWN;
     }
+
+    /**
+     * Put an entry for a host in the host resolver cache. This can save time
+     * when making requests to this host in the future by avoiding having to
+     * resolve the host.
+     * <p>
+     * <b>Caveats:</b>
+     * <ul>
+     * <li>Only add trustworthy entries. Incorrect entries can provoke
+     *     security vulnerabilities like man-in-the-middle attacks when SSL/TLS
+     *     is not used.</li>
+     * <li>Putting an entry in the cache evicts any previously existing entry
+     *     for the host.</li>
+     * <li>Hosts can resolve to different IP addresses accessible with varying
+     *     latencies. An entry placed in the cache accessible with high latency,
+     *     e.g. a far away server, can harm performance if normal host
+     *     resolution would have provided more optimal results, e.g. the address
+     *     of a nearby server.</li>
+     * <li>The entry may be purged from the cache prior to the given lifetime
+     *     when certain events happen, for example if the default network
+     *     connection changes.</li>
+     * </ul>
+     * @param hostName the name of the host to add an entry for.
+     * @param addresses the list of addresses to add for the host.
+     * @param secondsToLive the maximum number of seconds this entry should live
+     *            in the cache.
+     */
+    public void putHostCache(String hostName, InetAddress[] addresses, int secondsToLive) {}
 }