You can find a great tutorial to resolve your problem of multiline row HERE. This Tutorial is from Loiane Groner.
You just need to add this to your CSS file :
.x-grid-row .x-grid-cell-inner {
white-space: normal;
}
.x-grid-row-over .x-grid-cell-inner {
font-weight: bold;
white-space: normal;
}
Hope this will be helpfull for you!