decrementSingleComponent(component) {
let count = this.componentCount.get(component);
assert(typeof count === 'number');
assert(count > 0);
this.componentCount.set(component, count - 1);
}
hasComponent(component) {
return this.componentCount.get(component) > 0;
}
clearComponentCount() {
for (let i = 0; i < this.componentCount.length; ++i) {
this.componentCount.set(i, 0);
}
}