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

base/cancelable_callback.h

 // Copyright (c) 2011 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.
 //
 // CancelableCallback is a wrapper around base::Callback that allows
 // cancellation of a callback. CancelableCallback takes a reference on the
 // wrapped callback until this object is destroyed or Reset()/Cancel() are
 // called.
 //
 // NOTE:
@@ skipping 23 matching lines @@
 // CancelableClosure timeout(base::Bind(&TimeoutCallback, "Test timed out."));
 // MessageLoop::current()->PostDelayedTask(FROM_HERE, timeout.callback(),
 //                                         4000)  // 4 seconds to run.
 // RunIntensiveTest();
 // MessageLoop::current()->Run();
 // timeout.Cancel();  // Hopefully this is hit before the timeout callback runs.
 //
 
 #ifndef BASE_CANCELABLE_CALLBACK_H_
 #define BASE_CANCELABLE_CALLBACK_H_
-#pragma once
 
 #include "base/base_export.h"
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/callback_internal.h"
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/memory/weak_ptr.h"
 
 namespace base {
@@ skipping 139 matching lines @@
   base::Callback<void(A1)> callback_;
 
   DISALLOW_COPY_AND_ASSIGN(CancelableCallback);
 };
 
 typedef CancelableCallback<void(void)> CancelableClosure;
 
 }  // namespace base
 
 #endif  // BASE_CANCELABLE_CALLBACK_H_