Make the #includes consistent in various thread checkers between debug and release mode.

base/sequence_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_SEQUENCE_CHECKER_H_
 #define BASE_SEQUENCE_CHECKER_H_
 
-#include "base/memory/ref_counted.h"
-
 // See comments for the similar block in thread_checker.h.
 #if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
 #define ENABLE_SEQUENCE_CHECKER 1
 #else
 #define ENABLE_SEQUENCE_CHECKER 0
 #endif
 
-#if ENABLE_SEQUENCE_CHECKER
 #include "base/sequence_checker_impl.h"
-#endif
 
 namespace base {
 
-class SequencedTaskRunner;
-
 // Do nothing implementation, for use in release mode.
 //
 // Note: You should almost always use the SequenceChecker class to get
 // the right version for your build configuration.
 class SequenceCheckerDoNothing {
  public:
   bool CalledOnValidSequencedThread() const {
     return true;
   }
 
@@ skipping 10 matching lines @@
 //  public:
 //   void Foo() {
 //     DCHECK(sequence_checker_.CalledOnValidSequencedThread());
 //     ... (do stuff) ...
 //   }
 //
 //  private:
 //   SequenceChecker sequence_checker_;
 // }
 //
-// In Release mode, CalledOnValidSequence will always return true.
+// In Release mode, CalledOnValidSequencedThread() will always return true.
 #if ENABLE_SEQUENCE_CHECKER
 class SequenceChecker : public SequenceCheckerImpl {
 };
 #else
 class SequenceChecker : public SequenceCheckerDoNothing {
 };
 #endif  // ENABLE_SEQUENCE_CHECKER
 
 #undef ENABLE_SEQUENCE_CHECKER
 
 }  // namespace base
 
 #endif  // BASE_SEQUENCE_CHECKER_H_