Merge "libutils: better docs for sp<>::make"

public:

    inline sp() : m_ptr(nullptr) { }

    // TODO: switch everyone to using this over new, and make RefBase operator

    // new private to that class so that we can avoid RefBase being used with

    // other memory management mechanisms.

    // The old way of using sp<> was like this. This is bad because it relies

    // on implicit conversion to sp<>, which we would like to remove (if an

    // object is being managed some other way, this is double-ownership). We

    // want to move away from this:

    //

    //     sp<Foo> foo = new Foo(...); // DO NOT DO THIS

    //

    // Instead, prefer to do this:

    //

    //     sp<Foo> foo = sp<Foo>::make(...); // DO THIS

    //

    // Sometimes, in order to use this, when a constructor is marked as private,

    // you may need to add this to your class:

    //

    //     friend class sp<Foo>;

    template <typename... Args>

    static inline sp<T> make(Args&&... args);