mus: Add PointerWatcher for passively observing mouse and touch events

ash/shell_delegate.h

Index: ash/shell_delegate.h
diff --git a/ash/shell_delegate.h b/ash/shell_delegate.h
index e3c6f5f98e6d5bfc1154370c350aaabd5e53a0cc..24c92574d6bc77d817cc29e04eb2fb40bc75f46d 100644
--- a/ash/shell_delegate.h
+++ b/ash/shell_delegate.h
@@ -5,6 +5,7 @@
 #ifndef ASH_SHELL_DELEGATE_H_
 #define ASH_SHELL_DELEGATE_H_
 
+#include <memory>
 #include <string>
 
 #include "ash/ash_export.h"
@@ -40,6 +41,7 @@ namespace ash {
 class AccessibilityDelegate;
 class MediaDelegate;
 class NewWindowDelegate;
+class PointerWatcherDelegate;
 class SessionStateDelegate;
 class ShelfDelegate;
 class ShelfModel;
@@ -138,6 +140,9 @@ class ASH_EXPORT ShellDelegate {
   // Creates a media delegate. Shell takes ownership of the delegate.
   virtual MediaDelegate* CreateMediaDelegate() = 0;
 
+  virtual std::unique_ptr<PointerWatcherDelegate>
+  CreatePointerWatcherDelegate() = 0;
+
   // Creates a menu model for the |shelf| and optional shelf |item|.
   // If |item| is null, this creates a context menu for the desktop or shelf.
   virtual ui::MenuModel* CreateContextMenu(ash::Shelf* shelf,