Add GetActiveScreen to DisplayInfoProvider

chrome/browser/extensions/api/system_display/display_info_provider.h

 // Copyright 2013 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_EXTENSIONS_API_SYSTEM_DISPLAY_DISPLAY_INFO_PROVIDER_H_
 #define CHROME_BROWSER_EXTENSIONS_API_SYSTEM_DISPLAY_DISPLAY_INFO_PROVIDER_H_
 
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/linked_ptr.h"
 
 namespace gfx {
 class Display;
+class Screen;
 }
 
 namespace extensions {
 
 namespace api {
 namespace system_display {
 struct DisplayProperties;
 struct DisplayUnitInfo;
 }
 }
@@ skipping 13 matching lines @@
   // Using this in other tests (e.g. unit_tests) will result in DCHECK failure.
   static void InitializeForTesting(DisplayInfoProvider* display_info_provider);
 
   // Updates the display with |display_id| according to |info|. Returns whether
   // the display was successfully updated. On failure, no display parameters
   // should be changed, and |error| should be set to the error string.
   virtual bool SetInfo(const std::string& display_id,
                        const api::system_display::DisplayProperties& info,
                        std::string* error) = 0;
 
+  // Get the screen that is always active, which will be used for monitoring
+  // display changes events.
+  virtual gfx::Screen* GetActiveScreen() = 0;
+
   DisplayInfo GetAllDisplaysInfo();
 
  protected:
   DisplayInfoProvider();
 
  private:
   static DisplayInfoProvider* Create();
 
   // Update the content of the |unit| obtained for |display| using
   // platform specific method.
   virtual void UpdateDisplayUnitInfoForPlatform(
       const gfx::Display& display,
       api::system_display::DisplayUnitInfo* unit) = 0;
 
   DISALLOW_COPY_AND_ASSIGN(DisplayInfoProvider);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_SYSTEM_DISPLAY_DISPLAY_INFO_PROVIDER_H_