fast/dom/shadow/content-child-whitespace-between-span.html is crashing with IncrementalShadowDOM flag.

*#document                                   
        DOCTYPE html                         
        HTML                                 
                HEAD                         
                        #text "\n"           
                        STYLE                
                                #text "\nsummary { display: none; }\nspan { background-color: red; }\n"                                                                               
                        #text "\n"           
                #text "\n"                   
                BODY                         
                        #text "\n"           
                        DIV                  
                                #text "\n"   
                                DIV          
                                        #text "\n"                                         
                                        DETAILS                                            
                                                #shadow-root                               
                                                        CONTENT id="details-summary"       
                                                                SUMMARY                    
                                                                        #shadow-root       
                                                                                DIV id="details-marker"                                                                               
                                                                                CONTENT    
                                                                        #text "Details"    
                                                        DIV id="details-content"           
                                                                CONTENT                    
                                                #text "\n"                                 
                                                DIV                                        
                                                        #text "Hello1"                     
                                                #text "\n"                                 
                                                SPAN                                       
                                                        #text "Hello2"                     
                                                #text "\n"                                 
                                                SPAN                                       
                                                        #text "Hello3"                     
                                                #text "\n"                                 
                                                SUMMARY                                    
                                                        #shadow-root                       
                                                                DIV id="details-marker"    
                                                                CONTENT                    
                                                #text "\n"                                 
                                        #text "\n"                                         
                                #text "\n"   
                        #text "\n\n\n"