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

content/renderer/idle_user_detector.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.
 
 #ifndef CONTENT_RENDERER_IDLE_USER_DETECTOR_H_
 #define CONTENT_RENDERER_IDLE_USER_DETECTOR_H_
 
 #include "base/basictypes.h"
 #include "content/public/renderer/render_view_observer.h"
 
 namespace WebKit {
 class WebInputEvent;
 }
 
 namespace content {
 
 // Class which observes user input events and postpones
 // idle notifications if the user is active.
 class IdleUserDetector : public RenderViewObserver {
  public:
-  IdleUserDetector(RenderView* render_view);
+  explicit IdleUserDetector(RenderView* render_view);
   virtual ~IdleUserDetector();
 
  private:
   // RenderViewObserver implementation:
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
 
   void OnHandleInputEvent(const WebKit::WebInputEvent* event,
                           bool is_keyboard_shortcut);
 
   DISALLOW_COPY_AND_ASSIGN(IdleUserDetector);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_IDLE_USER_DETECTOR_H_