[DevTools] Show DropDownMenu for left mouse button only.

Source/devtools/front_end/ui/DropDownMenu.js

Index: Source/devtools/front_end/ui/DropDownMenu.js
diff --git a/Source/devtools/front_end/ui/DropDownMenu.js b/Source/devtools/front_end/ui/DropDownMenu.js
index 1448c89e55d0309040e383779b8c97d033d60722..201d61c9b049a1882750b0ac71f6079e4dbac191 100644
--- a/Source/devtools/front_end/ui/DropDownMenu.js
+++ b/Source/devtools/front_end/ui/DropDownMenu.js
@@ -29,6 +29,8 @@ WebInspector.DropDownMenu.prototype = {
      */
     _onMouseDown: function(event)
     {
+        if (event.which !== 1)
+            return;
         var menu = new WebInspector.ContextMenu(event);
         for (var item of this._items)
             menu.appendCheckboxItem(item.title, this._itemHandler.bind(this, item.id), item.id === this._selectedItemId);