40     assert(!head_);  in ~LRUList()
52     assert((!head_ && !tail_) || (head_ && tail_));  in Push()
53     assert(!head_ || !head_->prev_);  in Push()
56     t->next_ = head_;  in Push()
57     if (head_) {  in Push()
58       head_->prev_ = t;  in Push()
61     head_ = t;  in Push()
77     assert(tail_ && head_);  in Pop()
79     assert(!head_->prev_);  in Pop()
81     T* t = head_;  in Pop()
108     return !head_ && !tail_;  in IsEmpty()
118     assert(head_ && tail_);  in UnlinkImpl()
119     assert(t->prev_ || head_ == t);  in UnlinkImpl()
132     if (head_ == t) {  in UnlinkImpl()
133       head_ = head_->next_;  in UnlinkImpl()
152     assert((!head_ && !tail_) || (head_ && tail_));  in PushBackImpl()
153     assert(!head_ || !head_->prev_);  in PushBackImpl()
162     if (!head_) {  in PushBackImpl()
163       head_ = tail_;  in PushBackImpl()
168   T* head_ = nullptr;         // front (cold)  variable