Added a system caret used for accessibility on Windows.

ui/views/win/hwnd_message_handler_delegate.h

Index: ui/views/win/hwnd_message_handler_delegate.h
diff --git a/ui/views/win/hwnd_message_handler_delegate.h b/ui/views/win/hwnd_message_handler_delegate.h
index f5328c49e708efc084432f2be569f2f58ca99573..a6d20d739c8279d76044d44f5e026358faf8b5aa 100644
--- a/ui/views/win/hwnd_message_handler_delegate.h
+++ b/ui/views/win/hwnd_message_handler_delegate.h
@@ -16,6 +16,7 @@ class Size;
 
 namespace ui {
 class Accelerator;
+class InputMethodObserver;
 class KeyEvent;
 class MouseEvent;
 class TouchEvent;
@@ -33,6 +34,10 @@ enum class FrameMode {
 // notifications from the underlying HWND and service requests for data.
 class VIEWS_EXPORT HWNDMessageHandlerDelegate {
  public:
+  // Required for tracking the caret by some accessibility software.
+  virtual void AddInputMethodObserver(ui::InputMethodObserver* observer) = 0;

[sky, 2017/06/19 15:00:14]

How about exposing the InputMethod instead, e.g.
GetHWNDMessageDelegateInputMethod().

+  virtual void RemoveInputMethodObserver(ui::InputMethodObserver* observer) = 0;
+
   // True if the widget associated with this window has a non-client view.
   virtual bool HasNonClientView() const = 0;