Update from https://crrev.com/315085

base/threading/thread_checker.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.
 
 #ifndef BASE_THREADING_THREAD_CHECKER_H_
 #define BASE_THREADING_THREAD_CHECKER_H_
 
 // Apart from debug builds, we also enable the thread checker in
 // builds with DCHECK_ALWAYS_ON so that trybots and waterfall bots
 // with this define will get the same level of thread checking as
@@ skipping 12 matching lines @@
 #include "base/threading/thread_checker_impl.h"
 
 namespace base {
 
 // Do nothing implementation, for use in release mode.
 //
 // Note: You should almost always use the ThreadChecker class to get the
 // right version for your build configuration.
 class ThreadCheckerDoNothing {
  public:
-  bool CalledOnValidThread() const {
+  bool CalledOnValidThread() const WARN_UNUSED_RESULT {
     return true;
   }
 
   void DetachFromThread() {}
 };
 
 // ThreadChecker is a helper class used to help verify that some methods of a
 // class are called from the same thread. It provides identical functionality to
 // base::NonThreadSafe, but it is meant to be held as a member variable, rather
 // than inherited from base::NonThreadSafe.
@@ skipping 30 matching lines @@
 #else
 class ThreadChecker : public ThreadCheckerDoNothing {
 };
 #endif  // ENABLE_THREAD_CHECKER
 
 #undef ENABLE_THREAD_CHECKER
 
 }  // namespace base
 
 #endif  // BASE_THREADING_THREAD_CHECKER_H_