Fix a crash caused by invalid selection set by Undo command.

Source/core/editing/Editor.cpp

Index: Source/core/editing/Editor.cpp
diff --git a/Source/core/editing/Editor.cpp b/Source/core/editing/Editor.cpp
index f1044e816a0bd4b4274aaabdc61bc328b00aa359..5314562e3b67897ffd840a8cadc788845dfb678a 100644
--- a/Source/core/editing/Editor.cpp
+++ b/Source/core/editing/Editor.cpp
@@ -719,7 +719,8 @@ void Editor::unappliedEditing(PassRefPtrWillBeRawPtr<EditCommandComposition> cmd
 
     VisibleSelection newSelection(cmd->startingSelection());
     newSelection.validatePositionsIfNeeded();
-    changeSelectionAfterCommand(newSelection, FrameSelection::CloseTyping | FrameSelection::ClearTypingStyle);
+    if (newSelection.start().document() == m_frame.document() && newSelection.end().document() == m_frame.document())
+        changeSelectionAfterCommand(newSelection, FrameSelection::CloseTyping | FrameSelection::ClearTypingStyle);
 
     m_lastEditCommand = nullptr;
     if (UndoStack* undoStack = this->undoStack())