Fix some missing const reference on function parameter.

cc/resources/worker_pool_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 "cc/resources/worker_pool.h"
 
 #include "base/time/time.h"
 #include "cc/base/completion_event.h"
 #include "cc/test/lap_timer.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 142 matching lines @@
 
   // Overridden from testing::Test:
   virtual void SetUp() OVERRIDE {
     worker_pool_ = PerfWorkerPool::Create();
   }
   virtual void TearDown() OVERRIDE {
     worker_pool_->Shutdown();
     worker_pool_->CheckForCompletedTasks();
   }
 
-  void AfterTest(const std::string test_name) {
+  void AfterTest(const std::string& test_name) {
     // Format matches chrome/test/perf/perf_test.h:PrintResult
     printf(
         "*RESULT %s: %.2f runs/s\n", test_name.c_str(), timer_.LapsPerSecond());
   }
 
-  void RunScheduleTasksTest(const std::string test_name,
+  void RunScheduleTasksTest(const std::string& test_name,
                             unsigned max_depth,
                             unsigned num_children_per_node) {
     timer_.Reset();
     do {
       scoped_refptr<PerfControlWorkerPoolTaskImpl> leaf_task(
           new PerfControlWorkerPoolTaskImpl);
       worker_pool_->ScheduleTasks(
           NULL, leaf_task.get(), max_depth, num_children_per_node);
       leaf_task->WaitForTaskToStartRunning();
       worker_pool_->ScheduleTasks(NULL, NULL, 0, 0);
       worker_pool_->CheckForCompletedTasks();
       leaf_task->AllowTaskToFinish();
       timer_.NextLap();
     } while (!timer_.HasTimeLimitExpired());
 
     perf_test::PrintResult("schedule_tasks", "", test_name,
                            timer_.LapsPerSecond(), "runs/s", true);
   }
 
-  void RunExecuteTasksTest(const std::string test_name,
+  void RunExecuteTasksTest(const std::string& test_name,
                            unsigned max_depth,
                            unsigned num_children_per_node) {
     timer_.Reset();
     do {
       scoped_refptr<PerfControlWorkerPoolTaskImpl> root_task(
           new PerfControlWorkerPoolTaskImpl);
       worker_pool_->ScheduleTasks(
           root_task.get(), NULL, max_depth, num_children_per_node);
       root_task->WaitForTaskToStartRunning();
       root_task->AllowTaskToFinish();
@@ skipping 26 matching lines @@
   RunExecuteTasksTest("2_10", 2, 10);
   RunExecuteTasksTest("5_5", 5, 5);
   RunExecuteTasksTest("10_2", 10, 2);
   RunExecuteTasksTest("1000_1", 1000, 1);
   RunExecuteTasksTest("10_1", 10, 1);
 }
 
 }  // namespace
 
 }  // namespace cc