Add GetActiveScreen to DisplayInfoProvider

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

Index: chrome/browser/extensions/api/system_display/display_info_provider.h
diff --git a/chrome/browser/extensions/api/system_display/display_info_provider.h b/chrome/browser/extensions/api/system_display/display_info_provider.h
index bf578de590a10405aa8e2434416adb7f5b3fd7ed..96d198d9d75f1ddf5cb9302c38dc6f8dfb435b74 100644
--- a/chrome/browser/extensions/api/system_display/display_info_provider.h
+++ b/chrome/browser/extensions/api/system_display/display_info_provider.h
@@ -13,6 +13,7 @@
 
 namespace gfx {
 class Display;
+class Screen;
 }
 
 namespace extensions {
@@ -46,6 +47,10 @@ class DisplayInfoProvider {
                        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: