Add missing (and remove superfluous) 'explicit' from constructors.

base/threading/thread_collision_warner.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_COLLISION_WARNER_H_
 #define BASE_THREADING_THREAD_COLLISION_WARNER_H_
 
 #include <memory>
 
 #include "base/atomicops.h"
@@ skipping 126 matching lines @@
 };
 
 struct BASE_EXPORT DCheckAsserter : public AsserterBase {
   virtual ~DCheckAsserter() {}
   virtual void warn() OVERRIDE;
 };
 
 class BASE_EXPORT ThreadCollisionWarner {
  public:
   // The parameter asserter is there only for test purpose
-  ThreadCollisionWarner(AsserterBase* asserter = new DCheckAsserter())
+  explicit ThreadCollisionWarner(AsserterBase* asserter = new DCheckAsserter())
       : valid_thread_id_(0),
         counter_(0),
         asserter_(asserter) {}
 
   ~ThreadCollisionWarner() {
     delete asserter_;
   }
 
   // This class is meant to be used through the macro
   // DFAKE_SCOPED_LOCK_THREAD_LOCKED
@@ skipping 77 matching lines @@
   // Here only for class unit tests purpose, during the test I need to not
   // DCHECK but notify the collision with something else.
   AsserterBase* asserter_;
 
   DISALLOW_COPY_AND_ASSIGN(ThreadCollisionWarner);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_THREAD_COLLISION_WARNER_H_