Remove now-unnecessary wrappers around gfx::Screen::GetScreen()

extensions/shell/browser/shell_display_info_provider.h

 // Copyright 2014 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 EXTENSIONS_SHELL_BROWSER_SHELL_DISPLAY_INFO_PROVIDER_H_
 #define EXTENSIONS_SHELL_BROWSER_SHELL_DISPLAY_INFO_PROVIDER_H_
 
 #include "base/macros.h"
 #include "extensions/browser/api/system_display/display_info_provider.h"
 
 namespace extensions {
 
 class ShellDisplayInfoProvider : public DisplayInfoProvider {
  public:
   ShellDisplayInfoProvider();
   ~ShellDisplayInfoProvider() override;
 
   // DisplayInfoProvider implementation.
   bool SetInfo(const std::string& display_id,
                const api::system_display::DisplayProperties& info,
                std::string* error) override;
   void UpdateDisplayUnitInfoForPlatform(
       const gfx::Display& display,
       extensions::api::system_display::DisplayUnitInfo* unit) override;
-  gfx::Screen* GetActiveScreen() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ShellDisplayInfoProvider);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_SHELL_BROWSER_SHELL_DISPLAY_INFO_PROVIDER_H_