Third try at landing gRPC refactoring. Previous issue failed on the waterfall

components/cronet/ios/cronet_environment.cc

Index: components/cronet/ios/cronet_environment.cc
diff --git a/components/cronet/ios/cronet_environment.cc b/components/cronet/ios/cronet_environment.cc
index 0fef4af2e2266ab840e1b76a457f213ba763f5a6..f136118a789f40eb110fc0e6b52d33c3a05b8c79 100644
--- a/components/cronet/ios/cronet_environment.cc
+++ b/components/cronet/ios/cronet_environment.cc
@@ -96,10 +96,6 @@ class CronetURLRequestContextGetter : public net::URLRequestContextGetter {
 
 namespace cronet {
 
-bool CronetEnvironment::IsOnNetworkThread() {
-  return network_io_thread_->task_runner()->BelongsToCurrentThread();
-}
-
 void CronetEnvironment::PostToNetworkThread(
     const tracked_objects::Location& from_here,
     const base::Closure& task) {
@@ -297,7 +293,6 @@ void CronetEnvironment::InitializeOnNetworkThread() {
       new net::MappedHostResolver(
           net::HostResolver::CreateDefaultResolver(nullptr)));
 
-  mapped_host_resolver->SetRulesFromString(host_resolver_rules_);
   main_context_->set_host_resolver(mapped_host_resolver.release());
 
   if (!cert_verifier_)
@@ -400,4 +395,22 @@ std::vector<uint8_t> CronetEnvironment::GetHistogramDeltas() {
   return data;
 }
 
+void CronetEnvironment::SetHostResolverRules(const std::string& rules) {
+  base::WaitableEvent event(base::WaitableEvent::ResetPolicy::AUTOMATIC,
+                            base::WaitableEvent::InitialState::NOT_SIGNALED);
+  PostToNetworkThread(
+      FROM_HERE,
+      base::Bind(&CronetEnvironment::SetHostResolverRulesOnNetworkThread,
+                 base::Unretained(this), rules, &event));
+  event.Wait();
+}
+
+void CronetEnvironment::SetHostResolverRulesOnNetworkThread(
+    const std::string& rules,
+    base::WaitableEvent* event) {
+  static_cast<net::MappedHostResolver*>(main_context_->host_resolver())
+      ->SetRulesFromString(rules);
+  event->Signal();
+}
+
 }  // namespace cronet