Pass clickEvent to controlElement inside label if targetNode can't start selection

third_party/WebKit/Source/core/html/HTMLLabelElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2010 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 155 matching lines @@
     if (evt->IsMouseEvent() && ToMouseEvent(evt)->HasPosition()) {
       if (LocalFrame* frame = GetDocument().GetFrame()) {
         // Check if there is a selection and click is not on the
         // selection.
         if (GetLayoutObject() && GetLayoutObject()->IsSelectable() &&
             frame->Selection()
                 .ComputeVisibleSelectionInDOMTreeDeprecated()
                 .IsRange() &&
             !frame->GetEventHandler()
                  .GetSelectionController()
-                 .MouseDownWasSingleClickInSelection())
+                 .MouseDownWasSingleClickInSelection() &&
+            evt->target()->ToNode()->CanStartSelection())

[yosin_UTC9, 2017/05/08 03:25:56]

Regarding a comment of this condition: "Check if there is a selection and click
is not on the selection."
Should we check whether Event#srcElement is LABEL element or not?

           is_label_text_selected = true;
         // If selection is there and is single click i.e. text is
         // selected by dragging over label text, then return.
         // Click count >=2, meaning double click or triple click,
         // should pass click event to control element.
         // Only in case of drag, *neither* we pass the click event,
         // *nor* we focus the control element.
         if (is_label_text_selected && ToMouseEvent(evt)->ClickCount() == 1)
           return;
       }
@@ skipping 43 matching lines @@
 }
 
 void HTMLLabelElement::AccessKeyAction(bool send_mouse_events) {
   if (HTMLElement* element = control())
     element->AccessKeyAction(send_mouse_events);
   else
     HTMLElement::AccessKeyAction(send_mouse_events);
 }
 
 }  // namespace blink