Rewrite base::Bind into base::BindOnce on trivial cases in base

base/trace_event/trace_category_unittest.cc

 // Copyright 2016 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 <string.h>
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/lazy_instance.h"
@@ skipping 112 matching lines @@
   const int kNumThreads = 32;
   std::unique_ptr<Thread> threads[kNumThreads];
   for (int i = 0; i < kNumThreads; i++) {
     threads[i].reset(new Thread("test thread"));
     threads[i]->Start();
   }
   WaitableEvent sync_event(WaitableEvent::ResetPolicy::MANUAL,
                            WaitableEvent::InitialState::NOT_SIGNALED);
   for (int i = 0; i < kNumThreads; i++) {
     threads[i]->task_runner()->PostTask(
-        FROM_HERE, Bind(&TestRaceThreadMain, Unretained(&sync_event)));
+        FROM_HERE, BindOnce(&TestRaceThreadMain, Unretained(&sync_event)));
   }
   sync_event.Signal();
   for (int i = 0; i < kNumThreads; i++)
     threads[i]->Stop();
 
   int num_times_seen = 0;
   for (const TraceCategory& cat : GetAllCategories()) {
     if (strcmp(cat.name(), "__test_race") == 0)
       num_times_seen++;
   }
   ASSERT_EQ(1, num_times_seen);
 }
 
 }  // namespace trace_event
 }  // namespace base