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

content/renderer/render_widget_fullscreen.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 CONTENT_RENDERER_RENDER_WIDGET_FULLSCREEN_H_
 #define CONTENT_RENDERER_RENDER_WIDGET_FULLSCREEN_H_
 
 #include "content/renderer/render_widget.h"
 
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebWidget.h"
 
 namespace content {
 
 // TODO(boliu): Override non-supported methods with no-op? eg setWindowRect().
 class RenderWidgetFullscreen : public RenderWidget {
  public:
   virtual void show(WebKit::WebNavigationPolicy);
 
  protected:
-  RenderWidgetFullscreen(const WebKit::WebScreenInfo& screen_info);
+  explicit RenderWidgetFullscreen(const WebKit::WebScreenInfo& screen_info);
   virtual ~RenderWidgetFullscreen();
 
   virtual WebKit::WebWidget* CreateWebWidget();
 
   bool Init(int32 opener_id);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_WIDGET_FULLSCREEN_H_