Fix network service hanging with empty bodies.

content/public/test/browser_test_base.cc

Index: content/public/test/browser_test_base.cc
diff --git a/content/public/test/browser_test_base.cc b/content/public/test/browser_test_base.cc
index c95feb56f0cac3f93f875e048dc877333f0a6122..9aeb8729e80310d4589480fce0967815c45b8563 100644
--- a/content/public/test/browser_test_base.cc
+++ b/content/public/test/browser_test_base.cc
@@ -408,6 +408,7 @@ void BrowserTestBase::InitializeNetworkProcess() {
   mojom::NetworkServiceTestPtr network_service_test;
   ServiceManagerConnection::GetForProcess()->GetConnector()->BindInterface(
       mojom::kNetworkServiceName, &network_service_test);
+  mojo::SyncCallRestrictions::ScopedAllowSyncCall allow_sync_call;
   network_service_test->AddRules(std::move(mojo_rules));
 }