Added a system caret used for accessibility on Windows.

ui/views/widget/desktop_aura/desktop_window_tree_host_win.h

Index: ui/views/widget/desktop_aura/desktop_window_tree_host_win.h
diff --git a/ui/views/widget/desktop_aura/desktop_window_tree_host_win.h b/ui/views/widget/desktop_aura/desktop_window_tree_host_win.h
index 12d0616467073f48f93f5aae5c4643482db1caeb..1d80a273832631e0284f1d5523e58985e4ca76b9 100644
--- a/ui/views/widget/desktop_aura/desktop_window_tree_host_win.h
+++ b/ui/views/widget/desktop_aura/desktop_window_tree_host_win.h
@@ -20,6 +20,10 @@ class ScopedTooltipDisabler;
 }
 }
 
+namespace ui {
+class InputMethodObserver;
+}  // namespace ui
+
 namespace views {
 class DesktopDragDropClientWin;
 class HWNDMessageHandler;
@@ -132,6 +136,8 @@ class VIEWS_EXPORT DesktopWindowTreeHostWin
   void OnWindowHidingAnimationCompleted() override;
 
   // Overridden from HWNDMessageHandlerDelegate:
+  void AddInputMethodObserver(ui::InputMethodObserver& observer) override;
+  void RemoveInputMethodObserver(ui::InputMethodObserver& observer) override;
   bool HasNonClientView() const override;
   FrameMode GetFrameMode() const override;
   bool HasFrame() const override;