Added comment about layout thread exit workflow(Specifically:when will a Exit message be received )
Added comment about layout thread exit workflow(Specifically:when will a Exit message be received )

Added comment about layout thread exit workflow

Comments
Regarding  clarify layout-thread exit workflow (Specifically:when will a Exit message be received )

Added comment about layout thread exit workflow

larsbergstrom/servo,peterjoel/servo,saneyuki/servo,nnethercote/servo,peterjoel/servo,larsbergstrom/servo,szeged/servo,paulrouget/servo,splav/servo,notriddle/servo,notriddle/servo,notriddle/servo,szeged/servo,DominoTree/servo,emilio/servo,peterjoel/servo,nnethercote/servo,notriddle/servo,szeged/servo,DominoTree/servo,peterjoel/servo,peterjoel/servo,larsbergstrom/servo,paulrouget/servo,larsbergstrom/servo,nnethercote/servo,splav/servo,saneyuki/servo,szeged/servo,emilio/servo,emilio/servo,szeged/servo,pyfisch/servo,splav/servo,paulrouget/servo,paulrouget/servo,DominoTree/servo,DominoTree/servo,nnethercote/servo,splav/servo,pyfisch/servo,KiChjang/servo,saneyuki/servo,emilio/servo,larsbergstrom/servo,KiChjang/servo,larsbergstrom/servo,DominoTree/servo,szeged/servo,KiChjang/servo,notriddle/servo,larsbergstrom/servo,saneyuki/servo,paulrouget/servo,notriddle/servo,splav/servo,emilio/servo,saneyuki/servo,notriddle/servo,peterjoel/servo,szeged/servo,DominoTree/servo,emilio/servo,peterjoel/servo,szeged/servo,nnethercote/servo,notriddle/servo,saneyuki/servo,splav/servo,saneyuki/servo,paulrouget/servo,saneyuki/servo,paulrouget/servo,nnethercote/servo,larsbergstrom/servo,peterjoel/servo,KiChjang/servo,splav/servo,emilio/servo,KiChjang/servo,KiChjang/servo,notriddle/servo,emilio/servo,KiChjang/servo,pyfisch/servo,KiChjang/servo,szeged/servo,splav/servo,nnethercote/servo,splav/servo,paulrouget/servo,nnethercote/servo,emilio/servo,emilio/servo,KiChjang/servo,DominoTree/servo,pyfisch/servo,paulrouget/servo,DominoTree/servo,szeged/servo,nnethercote/servo,DominoTree/servo,splav/servo,larsbergstrom/servo,notriddle/servo,pyfisch/servo,peterjoel/servo,paulrouget/servo,pyfisch/servo,pyfisch/servo,KiChjang/servo,saneyuki/servo,pyfisch/servo,peterjoel/servo,DominoTree/servo,pyfisch/servo,pyfisch/servo,larsbergstrom/servo,nnethercote/servo,saneyuki/servo