Add Cronet experimental option for host cache persistence

components/cronet/android/cronet_url_request_context_adapter.cc

Index: components/cronet/android/cronet_url_request_context_adapter.cc
diff --git a/components/cronet/android/cronet_url_request_context_adapter.cc b/components/cronet/android/cronet_url_request_context_adapter.cc
index 5274d9e69b88fbfa28e1116a5cbc3956c95cf9df..1961958f48f50ddc001bc84677d9cdc134b59096 100644
--- a/components/cronet/android/cronet_url_request_context_adapter.cc
+++ b/components/cronet/android/cronet_url_request_context_adapter.cc
@@ -38,6 +38,7 @@
 #include "components/cronet/android/cert/proto/cert_verification.pb.h"
 #include "components/cronet/android/cronet_library_loader.h"
 #include "components/cronet/histogram_manager.h"
+#include "components/cronet/host_cache_persistence_manager.h"
 #include "components/cronet/url_request_context_config.h"
 #include "components/prefs/pref_change_registrar.h"
 #include "components/prefs/pref_filter.h"
@@ -114,6 +115,7 @@ class NetLogWithNetworkChangeEvents {
 static base::LazyInstance<NetLogWithNetworkChangeEvents>::Leaky g_net_log =
     LAZY_INSTANCE_INITIALIZER;
 
+const char kHostCache[] = "net.host_cache";

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

Can we add a comment? and can we change name to indicate what it is, e.g. by
adding a "PersistencePrefName" suffix?

[mgersh, 2017/06/26 23:21:44]

Done, but the inconsistency bothered me so I changed the others too.

 const char kHttpServerProperties[] = "net.http_server_properties";
 const char kNetworkQualities[] = "net.network_qualities";
 // Current version of disk storage.
@@ -643,7 +645,7 @@ void CronetURLRequestContextAdapter::InitializeOnNetworkThread(
                           std::unique_ptr<PrefFilter>());
     context_builder.SetFileTaskRunner(GetFileThread()->task_runner());
 
-    // Set up HttpServerPropertiesManager.
+    // Register prefs and set up the PrefService.
     PrefServiceFactory factory;
     factory.set_user_prefs(json_pref_store_);
     scoped_refptr<PrefRegistrySimple> registry(new PrefRegistrySimple());
@@ -654,8 +656,12 @@ void CronetURLRequestContextAdapter::InitializeOnNetworkThread(
       registry->RegisterDictionaryPref(kNetworkQualities,
                                        PrefRegistry::LOSSY_PREF);
     }
+    if (config->enable_host_cache_persistence) {
+      registry->RegisterListPref(kHostCache);
+    }
     pref_service_ = factory.Create(registry.get());
 
+    // Set up the HttpServerPropertiesManager.
     std::unique_ptr<net::HttpServerPropertiesManager>
         http_server_properties_manager(new net::HttpServerPropertiesManager(
             new PrefServiceAdapter(pref_service_.get()),
@@ -709,6 +715,17 @@ void CronetURLRequestContextAdapter::InitializeOnNetworkThread(
 
   context_ = context_builder.Build();
 
+  // Set up host cache persistence if it's enabled. Done after building the

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

nit: Done->Performed?  "Done" can be confused with an end state rather than the
action.

[mgersh, 2017/06/26 23:21:44]

Done. (And also performed.)

+  // URLRequestContext to get access to the HostCache.
+  if (!config->storage_path.empty() && config->enable_host_cache_persistence) {

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

Can we change the storage_path check to a check for pref_service_? 
pref_service_ is what HostCachePersistenceManager() will crash without and this
prevents problems if some part of the if-clause on lines 637-674 fails.

[mgersh, 2017/06/26 23:21:44]

Done.

+    net::HostCache* host_cache = context_->host_resolver()->GetHostCache();
+    host_cache_persistence_manager_ =
+        base::MakeUnique<HostCachePersistenceManager>(
+            host_cache, pref_service_.get(), kHostCache,
+            base::TimeDelta::FromMilliseconds(
+                config->host_cache_persistence_timer));
+  }
+
   context_->set_check_cleartext_permitted(true);
   context_->set_enable_brotli(config->enable_brotli);