Add Cronet experimental option for host cache persistence

components/cronet/android/test/experimental_options_test.cc

+// Copyright 2017 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.
+
+#include "components/cronet/android/test/experimental_options_test.h"
+
+#include <jni.h>
+
+#include "base/android/jni_android.h"
+#include "base/android/scoped_java_ref.h"
+#include "base/time/time.h"
+#include "components/cronet/android/test/cronet_test_util.h"
+#include "jni/ExperimentalOptionsTest_jni.h"
+#include "net/base/address_family.h"
+#include "net/base/net_errors.h"
+#include "net/dns/host_cache.h"
+#include "net/dns/host_resolver.h"
+#include "net/url_request/url_request_context.h"
+
+using base::android::JavaParamRef;
+
+namespace cronet {
+
+namespace {
+void WriteToHostCacheOnNetworkThread(jlong jcontext_adapter) {
+  net::URLRequestContext* context =
+      TestUtil::GetURLRequestContext(jcontext_adapter);
+  net::HostCache* cache = context->host_resolver()->GetHostCache();
+  net::HostCache::Key key("host-cache-test-host",
+                          net::ADDRESS_FAMILY_UNSPECIFIED, 0);
+  net::HostCache::Entry entry(net::OK, net::AddressList());

[pauljensen, 2017/06/26 16:37:17]

can we put in a legitimate IP address? like the one from
net::EmbeddedTestServer::GetAddressList().  Then can we augment the Java test to
fetch a resource from the EmbeddedTestServer, rewriting the hostname in the URL
to "host-cache-test-host"?  Then can we test the cache is persisted and then
reloaded, by fetching the resource again from a new CronetEngine instance once
the HostCache has been reloaded from persistence?  I feel like this would be a
fairly realistic test, and would be less fragile then looking for strings in the
prefs file (which could break if the prefs file implementation changed, e.g.
used compression).

[mgersh, 2017/06/26 23:21:45]

I like that idea. Thanks! Done.

+  cache->Set(key, entry, base::TimeTicks::Now(),
+             base::TimeDelta::FromSeconds(1));
+}
+}  // namespace
+
+static void WriteToHostCache(JNIEnv* env,
+                             const JavaParamRef<jclass>& jcaller,
+                             jlong jcontext_adapter) {
+  TestUtil::RunAfterContextInit(
+      jcontext_adapter,
+      base::Bind(&WriteToHostCacheOnNetworkThread, jcontext_adapter));
+}
+
+bool RegisterExperimentalOptionsTest(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+}  // namespace cronet