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 6099dc14adcae1bd2da71e88050a4607f7ec8ed9..3f1c7bffb61f426973561042ff4f9dcb57266b5c 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
@@ -19,9 +19,13 @@ class FocusClient;
 }
 }
 
+namespace ui {
+class InputMethod;
+}  // namespace ui
+
 namespace wm {
 class ScopedTooltipDisabler;
-}
+}  // namespace wm
 
 namespace views {
 class DesktopDragDropClientWin;
@@ -135,6 +139,7 @@ class VIEWS_EXPORT DesktopWindowTreeHostWin
   void OnWindowHidingAnimationCompleted() override;
 
   // Overridden from HWNDMessageHandlerDelegate:
+  ui::InputMethod* GetHWNDMessageDelegateInputMethod() override;
   bool HasNonClientView() const override;
   FrameMode GetFrameMode() const override;
   bool HasFrame() const override;