Make DisplayInfoProvider an interface

chrome/browser/extensions/BUILD.gn

 # 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.
 
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 
 gypi_values = exec_script(
     "//build/gypi_to_gn.py",
@@ skipping 172 matching lines @@
         gypi_values.chrome_browser_extensions_networking_private_sources,
         ".", "//chrome")
   }
 
   if (is_win) {
     deps += [
       "//third_party/iaccessible2",
       "//third_party/isimpledom",
     ]
   } else if (!is_chromeos) {
-    sources += [ "api/system_display/display_info_provider_aura.cc" ]
+    sources += [
+      "display_info_provider_aura.cc",
+      "display_info_provider_aura.h",
+    ]
   }
 
   if (enable_app_list) {
     sources += rebase_path(
         gypi_values.chrome_browser_extensions_app_list_sources,
         ".", "//chrome")
   }
 
   if (!use_ozone) {
     sources -= [
       "global_shortcut_listener_ozone.cc",
     ]
   }
 }