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

third_party/WebKit/Source/core/dom/Node.cpp

Index: third_party/WebKit/Source/core/dom/Node.cpp
diff --git a/third_party/WebKit/Source/core/dom/Node.cpp b/third_party/WebKit/Source/core/dom/Node.cpp
index eac5a1ca94a4456e3e673a3779c998f8b71beb00..a834c8b5463ed24fa606b1d574f35798798572cf 100644
--- a/third_party/WebKit/Source/core/dom/Node.cpp
+++ b/third_party/WebKit/Source/core/dom/Node.cpp
@@ -938,15 +938,21 @@ bool Node::canStartSelection() const
     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): Implement FlatTreeTraversal::ancestorsOf() and use it.
+    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),