public double getFractionOfRoot() {
    return fractionOfRoot;
  }
Gets how much of the root allocation each of the allocation units of this allocation accounts
for. The entire root allocation is {@code 1.0}.

@return the fraction of the root allocation this allocation's allocation units accounts for
jib-core/src/main/java/com/google/cloud/tools/jib/event/progress/Allocation.java