Replace WebIdlError enum with ParentMismatchError struct.
Replace WebIdlError enum with ParentMismatchError struct.

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