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

content/common/cc_messages_perftest.cc

 // Copyright 2013 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 "content/common/cc_messages.h"
 
 #include "base/test/launcher/unit_test_launcher.h"
 #include "base/test/test_suite.h"
 #include "cc/output/compositor_frame.h"
 #include "ipc/ipc_message.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/perf/perf_test.h"
 
 using cc::CompositorFrame;
 using cc::DelegatedFrameData;
 using cc::DrawQuad;
 using cc::PictureDrawQuad;
 using cc::RenderPass;
 using cc::SharedQuadState;
 
 namespace content {
 namespace {
 
 static const int kTimeLimitMillis = 2000;
 static const int kNumWarmupRuns = 20;
 static const int kTimeCheckInterval = 10;
 
 class CCMessagesPerfTest : public testing::Test {
  protected:
-  static void RunTest(std::string test_name, const CompositorFrame& frame) {
+  static void RunTest(const std::string& test_name,
+                      const CompositorFrame& frame) {
     for (int i = 0; i < kNumWarmupRuns; ++i) {
       IPC::Message msg(1, 2, IPC::Message::PRIORITY_NORMAL);
       IPC::ParamTraits<CompositorFrame>::Write(&msg, frame);
     }
 
     base::TimeTicks start = base::TimeTicks::Now();
     base::TimeTicks end =
         start + base::TimeDelta::FromMilliseconds(kTimeLimitMillis);
     base::TimeDelta min_time;
     int count = 0;
@@ skipping 102 matching lines @@
       quad->shared_quad_state = render_pass->shared_quad_state_list.back();
     }
     frame->delegated_frame_data->render_pass_list.push_back(render_pass.Pass());
   }
 
   RunTest("DelegatedFrame_ManyRenderPasses_10000_100", *frame);
 }
 
 }  // namespace
 }  // namespace content