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 bdfbaffcaa731d8793fc36b706dd527afbf48627..a1379adc80c6e402574af26066781f41fcdedd6d 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 AXSystemCaretWin;
+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;
@@ -227,6 +231,15 @@ 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,
@@ -574,6 +587,11 @@ class VIEWS_EXPORT HWNDMessageHandler :
   // px on activation loss to a window on the same monitor.
   void OnBackgroundFullscreen();
 
+  // Deletes the system caret used for accessibility. This will result in any
+  // clients that are still holding onto its |IAccessible| to get a failure code
+  // if they request its location.
+  void DestroyAXSystemCaret();
+
   HWNDMessageHandlerDelegate* delegate_;
 
   std::unique_ptr<FullscreenHandler> fullscreen_handler_;
@@ -698,6 +716,9 @@ 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::AXSystemCaretWin> ax_system_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.