struct has_linear_node_search_preference

Detects an 'absl_btree_prefer_linear_node_search' member. This is

a protocol used as an opt-in or opt-out of linear search.

For example, this would be useful for key types that wrap an integer

and define their own cheap operator

<

(). For example:

class K {

public:

using absl_btree_prefer_linear_node_search = std::true_type;

...

private:

friend bool operator

<

(K a, K b) { return a.k_

<

b.k_; }

int k_;

};

btree_map

<K

, V> m; // Uses linear search

If T has the preference tag, then it has a preference.

Btree will use the tag's truth value.