Added a system caret used for accessibility on Windows.

ui/views/win/hwnd_message_handler.h

Index: ui/views/win/hwnd_message_handler.h
diff --git a/ui/views/win/hwnd_message_handler.h b/ui/views/win/hwnd_message_handler.h
index f56a7ca05927ae0f5c947899aaeb522ca9db6667..f66478552a0ff13dec0478f6e01dfd20624ac9eb 100644
--- a/ui/views/win/hwnd_message_handler.h
+++ b/ui/views/win/hwnd_message_handler.h
@@ -21,6 +21,7 @@
 #include "base/win/scoped_gdi_object.h"
 #include "base/win/win_util.h"
 #include "ui/accessibility/ax_enums.h"
+#include "ui/base/ime/input_method_observer.h"
 #include "ui/base/ui_base_types.h"
 #include "ui/base/win/window_event_target.h"
 #include "ui/events/event.h"
@@ -38,6 +39,9 @@ class DirectManipulationHelper;
 }  // namespace gfx
 
 namespace ui  {
+class AXFakeCaretWin;
+class InputMethod;
+class TextInputClient;
 class ViewProp;
 }
 
@@ -117,9 +121,9 @@ const int WM_WINDOWSIZINGFINISHED = WM_USER;
 // used by both a views::NativeWidget and an aura::WindowTreeHost
 // implementation.
 // TODO(beng): This object should eventually *become* the WindowImpl.
-class VIEWS_EXPORT HWNDMessageHandler :
-    public gfx::WindowImpl,
-    public ui::WindowEventTarget {
+class VIEWS_EXPORT HWNDMessageHandler : public gfx::WindowImpl,
+                                        public ui::InputMethodObserver,
+                                        public ui::WindowEventTarget {
  public:
   explicit HWNDMessageHandler(HWNDMessageHandlerDelegate* delegate);
   ~HWNDMessageHandler() override;
@@ -222,6 +226,15 @@ class VIEWS_EXPORT HWNDMessageHandler :
   HICON GetSmallWindowIcon() const override;
   LRESULT OnWndProc(UINT message, WPARAM w_param, LPARAM l_param) override;
 
+  // Overridden from InputMethodObserver
+  void OnTextInputTypeChanged(const ui::TextInputClient* client) override {}
+  void OnFocus() override {}
+  void OnBlur() override {}
+  void OnCaretBoundsChanged(const ui::TextInputClient* client) override;
+  void OnTextInputStateChanged(const ui::TextInputClient* client) override;
+  void OnInputMethodDestroyed(const ui::InputMethod* input_method) override;
+  void OnShowImeIfNeeded() override {}
+
   // Overridden from WindowEventTarget
   LRESULT HandleMouseMessage(unsigned int message,
                              WPARAM w_param,
@@ -685,6 +698,9 @@ class VIEWS_EXPORT HWNDMessageHandler :
   std::unique_ptr<WindowsSessionChangeObserver>
       windows_session_change_observer_;
 
+  // Some assistive software need to track the location of the caret.
+  std::unique_ptr<ui::AXFakeCaretWin> ax_fake_caret_;
+
   // This class provides functionality to register the legacy window as a
   // Direct Manipulation consumer. This allows us to support smooth scroll
   // in Chrome on Windows 10.