[Editing][CSS] Drag from a -webkit-user-select:none element should not start selection

third_party/WebKit/Source/core/dom/Node.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, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 920 matching lines @@
 // FIXME: Shouldn't these functions be in the editing code?  Code that asks questions about HTML in the core DOM class
 // is obviously misplaced.
 bool Node::canStartSelection() const
 {
     if (isDisabledFormControl(this))
         return false;
 
     if (hasEditableStyle(*this))
         return true;
 
-    if (layoutObject()) {
-        const ComputedStyle& style = layoutObject()->styleRef();
-        // We allow selections to begin within an element that has -webkit-user-select: none set,
-        // but if the element is draggable then dragging should take priority over selection.
-        if (style.userDrag() == DRAG_ELEMENT && style.userSelect() == SELECT_NONE)
+    // We don't allow selections to begin within an element that has
+    // -webkit-user-select: none set,
+    // https://drafts.csswg.org/css-ui-4/#valdef-user-select-none
+    if (usedValueOfUserSelect(*this) == SELECT_NONE)
+        return false;
+
+    if (isHTMLElement() && toHTMLElement(this)->draggable())
+        return false;
+
+    // TODO(yoichio): Use FlatTreeTraversal::ancestorsOf().

[tkent, 2016/08/17 02:34:20]

Do you mean we don't have FlatTreeTraversal::ancestorsOf() yet?

+    for (const Node* parent = FlatTreeTraversal::parent(*this); parent; parent = FlatTreeTraversal::parent(*parent)) {
+        if (!parent->canStartSelection() && usedValueOfUserSelect(*parent) != SELECT_NONE)
             return false;
     }
-    ContainerNode* parent = FlatTreeTraversal::parent(*this);
-    return parent ? parent->canStartSelection() : true;
+    return true;
 }
 
 // StyledElements allow inline style (style="border: 1px"), presentational attributes (ex. color),
 // class names (ex. class="foo bar") and other non-basic styling features. They also control
 // if this element can participate in style sharing.
 //
 // FIXME: The only things that ever go through StyleResolver that aren't StyledElements are
 // PseudoElements and VTTElements. It's possible we can just eliminate all the checks
 // since those elements will never have class names, inline style, or other things that
 // this apparently guards against.
@@ skipping 1452 matching lines @@
 
 void showNodePath(const blink::Node* node)
 {
     if (node)
         node->showNodePathForThis();
     else
         fprintf(stderr, "Cannot showNodePath for (nil)\n");
 }
 
 #endif