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

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

Index: third_party/WebKit/Source/core/editing/commands/EditCommand.cpp
diff --git a/third_party/WebKit/Source/core/editing/commands/EditCommand.cpp b/third_party/WebKit/Source/core/editing/commands/EditCommand.cpp
index edd331acaec6f1a42234be86e8be348363c50f7e..e2dcf9bb437ee106acce98a8c9690030bb037211 100644
--- a/third_party/WebKit/Source/core/editing/commands/EditCommand.cpp
+++ b/third_party/WebKit/Source/core/editing/commands/EditCommand.cpp
@@ -102,7 +102,9 @@ bool EditCommand::isRenderedCharacter(const Position& position) {
 
 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) {