Remove #pragma once. Just from base/ for now.

base/test/task_runner_test_template.h

 // 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.
 
 // This class defines tests that implementations of TaskRunner should
 // pass in order to be conformant.  Here's how you use it to test your
 // implementation.
 //
 // Say your class is called MyTaskRunner.  Then you need to define a
 // class called MyTaskRunnerTestDelegate in my_task_runner_unittest.cc
@@ skipping 32 matching lines @@
 // Then you simply #include this file as well as gtest.h and add the
 // following statement to my_task_runner_unittest.cc:
 //
 //   INSTANTIATE_TYPED_TEST_CASE_P(
 //       MyTaskRunner, TaskRunnerTest, MyTaskRunnerTestDelegate);
 //
 // Easy!
 
 #ifndef BASE_TEST_TASK_RUNNER_TEST_TEMPLATE_H_
 #define BASE_TEST_TASK_RUNNER_TEST_TEMPLATE_H_
-#pragma once
 
 #include <cstddef>
 #include <map>
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "base/task_runner.h"
@@ skipping 143 matching lines @@
   EXPECT_EQ(expected_task_run_counts,
             this->task_tracker_->GetTaskRunCounts());
 }
 
 REGISTER_TYPED_TEST_CASE_P(
     TaskRunnerTest, Basic, Delayed, RunsTasksOnCurrentThread);
 
 }  // namespace base
 
 #endif  //#define BASE_TEST_TASK_RUNNER_TEST_TEMPLATE_H_