Added a system caret used for accessibility on Windows.

ui/views/win/hwnd_message_handler.cc

Index: ui/views/win/hwnd_message_handler.cc
diff --git a/ui/views/win/hwnd_message_handler.cc b/ui/views/win/hwnd_message_handler.cc
index 94ba71385f4323bd06674ea29a4fb9beabdf41cf..657b7aa666b0fcc196e9598d1b190533f885f234 100644
--- a/ui/views/win/hwnd_message_handler.cc
+++ b/ui/views/win/hwnd_message_handler.cc
@@ -20,8 +20,14 @@
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "base/trace_event/trace_event.h"
+#include "base/win/scoped_comptr.h"
 #include "base/win/scoped_gdi_object.h"
 #include "base/win/windows_version.h"
+#include "ui/accessibility/platform/ax_fake_caret_win.h"
+#include "ui/accessibility/platform/ax_platform_node_win.h"
+#include "ui/base/ime/input_method.h"
+#include "ui/base/ime/text_input_client.h"
+#include "ui/base/ime/text_input_type.h"
 #include "ui/base/view_prop.h"
 #include "ui/base/win/internal_constants.h"
 #include "ui/base/win/lock_state.h"
@@ -384,6 +390,7 @@ void HWNDMessageHandler::Init(HWND parent, const gfx::Rect& bounds) {
   prop_window_target_.reset(new ui::ViewProp(hwnd(),
                             ui::WindowEventTarget::kWin32InputEventTarget,
                             static_cast<ui::WindowEventTarget*>(this)));
+  delegate_->AddInputMethodObserver(*this);
 
   // Direct Manipulation is enabled on Windows 10+. The CreateInstance function
   // returns NULL if Direct Manipulation is not available.
@@ -929,6 +936,8 @@ LRESULT HWNDMessageHandler::OnWndProc(UINT message,
     delegate_->PostHandleMSG(message, w_param, l_param);
     if (message == WM_NCDESTROY) {
       RestoreEnabledIfNecessary();
+      delegate_->RemoveInputMethodObserver(*this);
+      ax_fake_caret_ = nullptr;

[sky, 2017/05/03 03:34:49]

Why do you need to explicitly destroy the caret? Please document that here.

       delegate_->HandleDestroyed();
     }
   }
@@ -939,6 +948,31 @@ LRESULT HWNDMessageHandler::OnWndProc(UINT message,
   return result;
 }
 
+void HWNDMessageHandler::OnCaretBoundsChanged(
+    const ui::TextInputClient* client) {
+  if (!client || client->GetTextInputType() == ui::TEXT_INPUT_TYPE_NONE)
+    return;
+  DCHECK(ax_fake_caret_);

[sky, 2017/05/03 03:34:49]

Move DCHECK closer to where it matters, line 961.

+  const gfx::Rect dip_caret_bounds(client->GetCaretBounds());
+  gfx::Rect caret_bounds =
+      display::win::ScreenWin::DIPToScreenRect(hwnd(), dip_caret_bounds);
+  // Collapse any selection.
+  caret_bounds.set_width(1);
+  ax_fake_caret_->MoveCaretTo(caret_bounds);

[sky, 2017/05/03 03:34:49]

If these bounds are in screen coordinates how are they updated when the HWND
moves?

+}
+
+void HWNDMessageHandler::OnTextInputStateChanged(
+    const ui::TextInputClient* client) {
+  if (!client || client->GetTextInputType() == ui::TEXT_INPUT_TYPE_NONE)
+    ax_fake_caret_ = nullptr;
+  ax_fake_caret_ = std::make_unique<ui::AXFakeCaretWin>(hwnd());
+}
+
+void HWNDMessageHandler::OnInputMethodDestroyed(
+    const ui::InputMethod* input_method) {
+  ax_fake_caret_ = nullptr;

[sky, 2017/05/03 03:34:49]

Remove observer?

+}
+
 LRESULT HWNDMessageHandler::HandleMouseMessage(unsigned int message,
                                                WPARAM w_param,
                                                LPARAM l_param,
@@ -1521,10 +1555,14 @@ LRESULT HWNDMessageHandler::OnGetObject(UINT message,
     // Retrieve MSAA dispatch object for the root view.
     base::win::ScopedComPtr<IAccessible> root(
         delegate_->GetNativeViewAccessible());
-
-    // Create a reference that MSAA will marshall to the client.
     reference_result = LresultFromObject(IID_IAccessible, w_param,
         static_cast<IAccessible*>(root.Detach()));
+  } else if (::GetFocus() == hwnd() && ax_fake_caret_ &&
+             static_cast<DWORD>(OBJID_CARET) == obj_id) {
+    base::win::ScopedComPtr<IAccessible> fake_caret_accessible =
+        ax_fake_caret_->GetCaret();
+    reference_result = LresultFromObject(IID_IAccessible, w_param,
+                                         fake_caret_accessible.Detach());

[sky, 2017/05/03 03:34:49]

How is this associated with lifetime of ax_fake_caret?

   }
 
   return reference_result;