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

net/base/prioritized_dispatcher_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <ctype.h>
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 135 matching lines @@
     return job;
   }
 
   TestJob* AddJobAtHead(char data, Priority priority) {
     TestJob* job = new TestJob(dispatcher_.get(), data, priority, &log_);
     jobs_.push_back(job);
     job->Add(true);
     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_);
     log_.clear();
   }
 
   std::string log_;
   scoped_ptr<PrioritizedDispatcher> dispatcher_;
   ScopedVector<TestJob> jobs_;
 };
@@ skipping 374 matching lines @@
   PrioritizedDispatcher::Handle handle = job_b->handle();
   ASSERT_FALSE(handle.is_null());
   dispatcher_->Cancel(handle);
   EXPECT_DEBUG_DEATH(dispatcher_->Cancel(handle), "");
 }
 #endif  // GTEST_HAS_DEATH_TEST && !defined(NDEBUG)
 
 }  // namespace
 
 }  // namespace net