Copy into arg.
Source
Matrix4 copyInto(Matrix4 arg) {
final argStorage = arg._m4storage;
argStorage[0] = _m4storage[0];
argStorage[1] = _m4storage[1];
argStorage[2] = _m4storage[2];
argStorage[3] = _m4storage[3];
argStorage[4] = _m4storage[4];
argStorage[5] = _m4storage[5];
argStorage[6] = _m4storage[6];
argStorage[7] = _m4storage[7];
argStorage[8] = _m4storage[8];
argStorage[9] = _m4storage[9];
argStorage[10] = _m4storage[10];
argStorage[11] = _m4storage[11];
argStorage[12] = _m4storage[12];
argStorage[13] = _m4storage[13];
argStorage[14] = _m4storage[14];
argStorage[15] = _m4storage[15];
return arg;
}