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

chrome/browser/ui/cocoa/download/background_theme.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 CHROME_BROWSER_UI_COCOA_DOWNLOAD_BACKGROUND_THEME_H_
 #define CHROME_BROWSER_UI_COCOA_DOWNLOAD_BACKGROUND_THEME_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/memory/scoped_nsobject.h"
 #include "ui/base/theme_provider.h"
 
 class BackgroundTheme : public ui::ThemeProvider {
  public:
-  BackgroundTheme(ui::ThemeProvider* provider);
+  explicit BackgroundTheme(ui::ThemeProvider* provider);
   virtual ~BackgroundTheme();
 
   // Overridden from ui::ThemeProvider:
   virtual gfx::ImageSkia* GetImageSkiaNamed(int id) const OVERRIDE;
   virtual SkColor GetColor(int id) const OVERRIDE;
   virtual bool GetDisplayProperty(int id, int* result) const OVERRIDE;
   virtual bool ShouldUseNativeFrame() const OVERRIDE;
   virtual bool HasCustomImage(int id) const OVERRIDE;
   virtual base::RefCountedMemory* GetRawData(
       int id,
       ui::ScaleFactor scale_factor) const OVERRIDE;
   virtual NSImage* GetNSImageNamed(int id, bool allow_default) const OVERRIDE;
   virtual NSColor* GetNSImageColorNamed(int id,
                                         bool allow_default) const OVERRIDE;
   virtual NSColor* GetNSColor(int id, bool allow_default) const OVERRIDE;
   virtual NSColor* GetNSColorTint(int id, bool allow_default) const OVERRIDE;
   virtual NSGradient* GetNSGradient(int id) const OVERRIDE;
 
  private:
   ui::ThemeProvider* provider_;
   scoped_nsobject<NSGradient> buttonGradient_;
   scoped_nsobject<NSGradient> buttonPressedGradient_;
   scoped_nsobject<NSColor> borderColor_;
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_DOWNLOAD_BACKGROUND_THEME_H_