Moved NavigationManagerImpl serialization out of CRWSessionController.

ios/web/public/test/fakes/test_web_state.mm

Index: ios/web/public/test/fakes/test_web_state.mm
diff --git a/ios/web/public/test/fakes/test_web_state.mm b/ios/web/public/test/fakes/test_web_state.mm
index 8114e4146d02e8b5737ce1ce0297497b0602a42f..276472f269c13661a69bde40962e428b9a85da75 100644
--- a/ios/web/public/test/fakes/test_web_state.mm
+++ b/ios/web/public/test/fakes/test_web_state.mm
@@ -68,6 +68,11 @@
   return navigation_manager_.get();
 }
 
+CRWNavigationManagerSerialization*
+TestWebState::BuildSerializedNavigationManager() {
+  return nil;
+}
+
 void TestWebState::SetNavigationManager(
     std::unique_ptr<NavigationManager> navigation_manager) {
   navigation_manager_ = std::move(navigation_manager);