SetItemWeight
BGroupLayout::SetItemWeight(int32 index, float weight)
BSplitLayout::SetItemWeight(int32 index, float weight, bool invalidateLayout)
BSplitLayout::SetItemWeight(BLayoutItem* item, float weight)
BSplitView::SetItemWeight(int32 index, float weight, bool invalidateLayout)
BSplitView::SetItemWeight(BLayoutItem* item, float weight)