[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 8ca374741da2815c1f830381cb91356aa97b4f5b..abbd80af3970f506d38b6ded77decde00a059c89 100644
--- a/third_party/WebKit/Source/core/editing/commands/EditCommand.cpp
+++ b/third_party/WebKit/Source/core/editing/commands/EditCommand.cpp
@@ -112,7 +112,8 @@ bool EditCommand::isRenderedCharacter(const Position& position)
 void EditCommand::setParent(CompositeEditCommand* parent)
 {
     DCHECK((parent && !m_parent) || (!parent && m_parent));
-    DCHECK(!parent || !isCompositeEditCommand() || !toCompositeEditCommand(this)->composition());
+    // 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;