Nits follow-up to TaskToken CL

base/sequence_token.h

 // 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.
 
 #ifndef BASE_SEQUENCE_TOKEN_H_
 #define BASE_SEQUENCE_TOKEN_H_
 
 #include "base/base_export.h"
 #include "base/macros.h"
 
@@ skipping 21 matching lines @@
   // Returns a valid SequenceToken which isn't equal to any previously returned
   // SequenceToken.
   static SequenceToken Create();
 
   // Returns the SequenceToken associated with the task running on the current
   // thread, as determined by the active ScopedSetSequenceTokenForCurrentThread
   // if any.
   static SequenceToken GetForCurrentThread();
 
  private:
-  SequenceToken(int token) : token_(token) {}
+  explicit SequenceToken(int token) : token_(token) {}
 
   static constexpr int kInvalidSequenceToken = -1;
   int token_ = kInvalidSequenceToken;
 };
 
 // A token that identifies a task.
 //
 // This is used by ThreadCheckerImpl to determine whether calls to
 // CalledOnValidThread() come from the same task and hence are deterministically
 // single-threaded (vs. calls coming from different sequenced or parallel tasks,
@@ skipping 17 matching lines @@
 
   // In the scope of a ScopedSetSequenceTokenForCurrentThread, returns a valid
   // TaskToken which isn't equal to any TaskToken returned in the scope of a
   // different ScopedSetSequenceTokenForCurrentThread. Otherwise, returns an
   // invalid TaskToken.
   static TaskToken GetForCurrentThread();
 
  private:
   friend class ScopedSetSequenceTokenForCurrentThread;
 
-  TaskToken(int token) : token_(token) {}
+  explicit TaskToken(int token) : token_(token) {}
 
   // Returns a valid TaskToken which isn't equal to any previously returned
   // TaskToken. This is private as it only meant to be instantiated by
   // ScopedSetSequenceTokenForCurrentThread.
   static TaskToken Create();
 
   static constexpr int kInvalidTaskToken = -1;
   int token_ = kInvalidTaskToken;
 };
 
@@ skipping 11 matching lines @@
  private:
   const SequenceToken sequence_token_;
   const TaskToken task_token_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedSetSequenceTokenForCurrentThread);
 };
 
 }  // namespace base
 
 #endif  // BASE_SEQUENCE_TOKEN_H_