Fixes leak of NativeTextfieldWin. The underlying HWND was getting

ui/views/controls/textfield/native_textfield_win.cc

Index: ui/views/controls/textfield/native_textfield_win.cc
diff --git a/ui/views/controls/textfield/native_textfield_win.cc b/ui/views/controls/textfield/native_textfield_win.cc
index b6fb41d202c8b2769fbbdf889cace1073872d653..dc36ebfb60e47bd84ab8b5dda67dcabb15b299e1 100644
--- a/ui/views/controls/textfield/native_textfield_win.cc
+++ b/ui/views/controls/textfield/native_textfield_win.cc
@@ -1084,6 +1084,10 @@ void NativeTextfieldWin::OnSysChar(TCHAR ch, UINT repeat_count, UINT flags) {
     SetMsgHandled(false);
 }
 
+void NativeTextfieldWin::OnFinalMessage(HWND hwnd) {
+  delete this;
+}
+
 void NativeTextfieldWin::HandleKeystroke() {
   const MSG* msg = GetCurrentMessage();
   ScopedFreeze freeze(this, GetTextObjectModel());