[InputEvent] Support |deleteByDrag|, |insertFromDrop| and fire in sequential order

third_party/WebKit/Source/core/editing/commands/EditCommand.cpp

 /*
  * Copyright (C) 2005, 2006, 2007 Apple, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 84 matching lines @@
   LayoutObject* layoutObject = position.anchorNode()->layoutObject();
   if (!layoutObject)
     return false;
 
   return toLayoutText(layoutObject)
       ->isRenderedCharacter(position.offsetInContainerNode());
 }
 
 void EditCommand::setParent(CompositeEditCommand* parent) {
   DCHECK((parent && !m_parent) || (!parent && m_parent));
-  DCHECK(!parent || !isCompositeEditCommand() ||
+  // Currently only allow merging |InsertFromDrop| and |DeleteByDrag| with |DragAndDropCommand| after applied.
+  DCHECK(!parent || parent->isCommandGroupWrapper() ||
+         !isCompositeEditCommand() ||
          !toCompositeEditCommand(this)->composition());
   m_parent = parent;
   if (parent) {
     m_startingSelection = parent->m_endingSelection;
     m_endingSelection = parent->m_endingSelection;
   }
 }
 
 void SimpleEditCommand::doReapply() {
   EditingState editingState;
   doApply(&editingState);
 }
 
 DEFINE_TRACE(EditCommand) {
   visitor->trace(m_document);
   visitor->trace(m_startingSelection);
   visitor->trace(m_endingSelection);
   visitor->trace(m_parent);
 }
 
 }  // namespace blink