int initialize(int nextAvailableRegister) {
    this.reg = nextAvailableRegister;
    this.spec = RegisterSpec.make(nextAvailableRegister, type.ropType);
    return size();
  }
Assigns registers to this local.

@return the number of registers required.
android/android_framework/dex-maker/src/main/java/com/android/dx/Local.java