Large Cursor: Add the toggle menuitem to a11y menu in uber tray

ash/shell_delegate.h

Index: ash/shell_delegate.h
diff --git a/ash/shell_delegate.h b/ash/shell_delegate.h
index 9aec503f6cfc88dbcf307926ac0cb7c2138d0f05..f9f6bf8779ba98ad734567b53801c226ed54d2d4 100644
--- a/ash/shell_delegate.h
+++ b/ash/shell_delegate.h
@@ -182,6 +182,12 @@ class ASH_EXPORT ShellDelegate {
   // Returns the current screen magnifier mode.
   virtual MagnifierType GetMagnifierType() const = 0;
 
+  // Invoked to enable Large Cursor.
+  virtual void SetLargeCursorEnabled(bool enabled) = 0;
+
+  // Returns if Large Cursor is enabled or not.
+  virtual bool IsLargeCursorEnabled() const = 0;
+
   // Returns true if the user want to show accesibility menu even when all the
   // accessibility features are disabled.
   virtual bool ShouldAlwaysShowAccessibilityMenu() const = 0;