DNS: Add stubs for persisting data across restarts

net/dns/host_resolver_impl.cc

Index: net/dns/host_resolver_impl.cc
diff --git a/net/dns/host_resolver_impl.cc b/net/dns/host_resolver_impl.cc
index 2345dad8c741a17ab5ca385cf92380be2f90ef8c..a1d3577fbd41818e9a7edef51e6fc9a126796eeb 100644
--- a/net/dns/host_resolver_impl.cc
+++ b/net/dns/host_resolver_impl.cc
@@ -499,6 +499,9 @@ void MakeNotStale(HostCache::EntryStaleness* stale_info) {
   stale_info->stale_hits = 0;
 }
 
+// Persist data every five minutes (potentially, cache and learned RTT).
+const int64_t kPersistDelaySec = 300;
+
 }  // namespace
 
 //-----------------------------------------------------------------------------
@@ -1759,6 +1762,8 @@ class HostResolverImpl::Job : public PrioritizedDispatcher::Job,
     net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
                                       entry.error());
 
+    resolver_->SchedulePersist();
+
     DCHECK(!requests_.empty());
 
     if (entry.error() == OK) {
@@ -1984,6 +1989,7 @@ HostResolverImpl::HostResolverImpl(
       additional_resolver_flags_(0),
       fallback_to_proctask_(true),
       worker_task_runner_(std::move(worker_task_runner)),
+      persist_initialized_(false),
       weak_ptr_factory_(this),
       probe_weak_ptr_factory_(this) {
   if (options.enable_caching)
@@ -2555,4 +2561,34 @@ void HostResolverImpl::SetDnsClient(std::unique_ptr<DnsClient> dns_client) {
   AbortDnsTasks();
 }
 
+void HostResolverImpl::InitializePersistence(
+    const PersistCallback& persist_callback,
+    std::unique_ptr<const base::Value> old_data) {
+  DCHECK(!persist_initialized_);
+  persist_callback_ = persist_callback;
+  persist_initialized_ = true;
+  if (old_data)
+    ApplyPersistentData(std::move(old_data));
+}
+
+void HostResolverImpl::SchedulePersist() {
+  if (!persist_initialized_ || persist_timer_.IsRunning())
+    return;
+  persist_timer_.Start(
+      FROM_HERE, base::TimeDelta::FromSeconds(kPersistDelaySec),
+      base::Bind(&HostResolverImpl::DoPersist, weak_ptr_factory_.GetWeakPtr()));
+}
+
+void HostResolverImpl::DoPersist() {
+  DCHECK(persist_initialized_);
+  persist_callback_.Run(GetPersistentData());
+}
+
+void HostResolverImpl::ApplyPersistentData(
+    std::unique_ptr<const base::Value> data) {}
+
+std::unique_ptr<const base::Value> HostResolverImpl::GetPersistentData() {
+  return std::unique_ptr<const base::Value>();
+}
+
 }  // namespace net