Added a class acting as a fake caret for accessibility.

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 1dbcea22c11137511a37a9d744ab15e6b0b1e8ff..a037be36e3f44b07b4cbc2240c271a4476c931a2 100644
--- a/ui/views/win/hwnd_message_handler.cc
+++ b/ui/views/win/hwnd_message_handler.cc
@@ -4,6 +4,8 @@
 
 #include "ui/views/win/hwnd_message_handler.h"
 
+#include <atlbase.h>
+#include <atlcom.h>
 #include <dwmapi.h>
 #include <oleacc.h>
 #include <shellapi.h>
@@ -22,6 +24,7 @@
 #include "base/trace_event/trace_event.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/base/view_prop.h"
 #include "ui/base/win/internal_constants.h"
 #include "ui/base/win/lock_state.h"
@@ -1510,10 +1513,14 @@ 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 (static_cast<DWORD>(OBJID_CARET) == obj_id) {
+    // Used by some assistive software to retrieve the location of the caret.
+    CComObjectStack<ui::AXFakeCaretWin> fake_caret;
+    DCHECK_EQ(fake_caret.m_hResFinalConstruct, S_OK);
+    reference_result = LresultFromObject(
+        IID_IAccessible, w_param, static_cast<IAccessible*>(&fake_caret));
   }
 
   return reference_result;