Cleanup: Pass std::string as const reference if possible

content/child/resource_dispatcher_unittest.cc

Index: content/child/resource_dispatcher_unittest.cc
diff --git a/content/child/resource_dispatcher_unittest.cc b/content/child/resource_dispatcher_unittest.cc
index 84c67fe63745e8b26142ef4b53f58136b2236814..fc1cb16e8a3db870c29562db2fb043658e141264 100644
--- a/content/child/resource_dispatcher_unittest.cc
+++ b/content/child/resource_dispatcher_unittest.cc
@@ -299,7 +299,7 @@ class ResourceDispatcherTest : public testing::Test, public IPC::Sender {
                                   shared_memory->requested_size(), 0)));
   }
 
-  void NotifyDataReceived(int request_id, std::string data) {
+  void NotifyDataReceived(int request_id, const std::string& data) {
     ASSERT_LE(data.length(), shared_memory_map_[request_id]->requested_size());
     memcpy(shared_memory_map_[request_id]->memory(), data.c_str(),
            data.length());