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

net/base/prioritized_dispatcher_unittest.cc

Index: net/base/prioritized_dispatcher_unittest.cc
diff --git a/net/base/prioritized_dispatcher_unittest.cc b/net/base/prioritized_dispatcher_unittest.cc
index 032a905fd715d10f53a9499b6ee39a5c943ea1ac..185937fd104f73f84f5d4eb3f14c70152cc0a52e 100644
--- a/net/base/prioritized_dispatcher_unittest.cc
+++ b/net/base/prioritized_dispatcher_unittest.cc
@@ -153,7 +153,7 @@ class PrioritizedDispatcherTest : public testing::Test {
     return job;
   }
 
-  void Expect(std::string log) {
+  void Expect(const std::string& log) {
     EXPECT_EQ(0u, dispatcher_->num_queued_jobs());
     EXPECT_EQ(0u, dispatcher_->num_running_jobs());
     EXPECT_EQ(log, log_);