arc: Implement scrollable OptIn window content.

chrome/browser/chromeos/arc/arc_support_host.h

Index: chrome/browser/chromeos/arc/arc_support_host.h
diff --git a/chrome/browser/chromeos/arc/arc_support_host.h b/chrome/browser/chromeos/arc/arc_support_host.h
index a7164e3d47fb19ef34c1e495f509f14d41490884..75d786ad4b092402baf3b5b807006bb7872fb735 100644
--- a/chrome/browser/chromeos/arc/arc_support_host.h
+++ b/chrome/browser/chromeos/arc/arc_support_host.h
@@ -9,10 +9,12 @@
 #include "chrome/browser/chromeos/arc/arc_auth_service.h"
 #include "components/prefs/pref_change_registrar.h"
 #include "extensions/browser/api/messaging/native_message_host.h"
+#include "ui/display/display_observer.h"
 
 // Supports communication with Arc support dialog.
 class ArcSupportHost : public extensions::NativeMessageHost,
-                       public arc::ArcAuthService::Observer {
+                       public arc::ArcAuthService::Observer,
+                       public display::DisplayObserver {
  public:
   static const char kHostName[];
   static const char kHostAppId[];
@@ -33,6 +35,12 @@ class ArcSupportHost : public extensions::NativeMessageHost,
   void OnOptInUIShowPage(arc::ArcAuthService::UIPage page,
                          const base::string16& status) override;
 
+  // display::DisplayObserver:
+  void OnDisplayAdded(const display::Display& new_display) override;
+  void OnDisplayRemoved(const display::Display& old_display) override;
+  void OnDisplayMetricsChanged(const display::Display& display,
+                               uint32_t changed_metrics) override;
+
  private:
   ArcSupportHost();