Added a class acting as a fake caret for accessibility.

ui/views/win/hwnd_message_handler.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_VIEWS_WIN_HWND_MESSAGE_HANDLER_H_
 #define UI_VIEWS_WIN_HWND_MESSAGE_HANDLER_H_
 
 #include <windows.h>
 
 #include <stddef.h>
 #include <map>
 #include <memory>
 #include <set>
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/strings/string16.h"
 #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"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/sequential_id_generator.h"
 #include "ui/gfx/win/window_impl.h"
 #include "ui/views/views_export.h"
 
 namespace gfx {
 class ImageSkia;
 class Insets;
 namespace win {
 class DirectManipulationHelper;
 }  // namespace win
 }  // namespace gfx
 
 namespace ui  {
+class AXFakeCaretWin;
+class InputMethod;
+class TextInputClient;
 class ViewProp;
 }
 
 namespace views {
 
 class FullscreenHandler;
 class HWNDMessageHandlerDelegate;
 class WindowsSessionChangeObserver;
 
 // These two messages aren't defined in winuser.h, but they are sent to windows
@@ skipping 61 matching lines @@
       case 0:
 
 // An object that handles messages for a HWND that implements the views
 // "Custom Frame" look. The purpose of this class is to isolate the windows-
 // specific message handling from the code that wraps it. It is intended to be
 // 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::InputMethodObserver,
     public ui::WindowEventTarget {
  public:
   explicit HWNDMessageHandler(HWNDMessageHandlerDelegate* delegate);
   ~HWNDMessageHandler() override;
 
   void Init(HWND parent, const gfx::Rect& bounds);
   void InitModalType(ui::ModalType modal_type);
 
   void Close();
   void CloseNow();
@@ skipping 83 matching lines @@
 
  private:
   typedef std::set<DWORD> TouchIDs;
   enum class DwmFrameState { OFF, ON };
 
   // Overridden from WindowImpl:
   HICON GetDefaultWindowIcon() const override;
   HICON GetSmallWindowIcon() const override;
   LRESULT OnWndProc(UINT message, WPARAM w_param, LPARAM l_param) override;
 
+  // Overridden from InputMethodObserver
+  void OnTextInputTypeChanged(const TextInputClient* client) override {}

[dmazzoni, 2017/04/27 05:07:32]

You should handle this in order to handle the case where the caret
disappears, i.e. focus moves to something that's not text.

+  void OnFocus() override {}
+  void OnBlur() override {}
+  void OnCaretBoundsChanged(const TextInputClient* client) override;
+  void OnTextInputStateChanged(const TextInputClient* client) override;
+  void OnInputMethodDestroyed(const InputMethod* input_method) override;

[dmazzoni, 2017/04/27 05:07:32]

Possibly this too.

See chrome/browser/chromeos/accessibility/accessibility_highlight_manager.cc
for another class where I extended InputMethodObserver to do focus highlighting,
you should follow similar logic

+  void OnShowImeIfNeeded() override {}
+
   // Overridden from WindowEventTarget
   LRESULT HandleMouseMessage(unsigned int message,
                              WPARAM w_param,
                              LPARAM l_param,
                              bool* handled) override;
   LRESULT HandleKeyboardMessage(unsigned int message,
                                 WPARAM w_param,
                                 LPARAM l_param,
                                 bool* handled) override;
   LRESULT HandleTouchMessage(unsigned int message,
@@ skipping 443 matching lines @@
   bool sent_window_size_changing_;
 
   // This is used to keep track of whether a WM_WINDOWPOSCHANGED has
   // been received after the WM_WINDOWPOSCHANGING.
   uint32_t current_window_size_message_ = 0;
 
   // Manages observation of Windows Session Change messages.
   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.
   std::unique_ptr<gfx::win::DirectManipulationHelper>
       direct_manipulation_helper_;
 
   // The location where the user clicked on the caption. We cache this when we
   // receive the WM_NCLBUTTONDOWN message. We use this in the subsequent
   // WM_NCMOUSEMOVE message to see if the mouse actually moved.
   // Please refer to the HandleMouseEventInternal function for details on why
@@ skipping 23 matching lines @@
 
   // The factory used with BEGIN_SAFE_MSG_MAP_EX.
   base::WeakPtrFactory<HWNDMessageHandler> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(HWNDMessageHandler);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIN_HWND_MESSAGE_HANDLER_H_