dynamic imports fix  for non-webpack environments. (#3414)
dynamic imports fix  for non-webpack environments. (#3414)

* Added condition to check whether method exists or not

* Conditional loop based on feature detection

* Added code comments as requested by the author

JeromeFitz/next.js,flybayer/next.js,JeromeFitz/next.js,BlancheXu/test,JeromeFitz/next.js,BlancheXu/test,zeit/next.js,BlancheXu/test,azukaru/next.js,JeromeFitz/next.js,azukaru/next.js,azukaru/next.js,zeit/next.js,azukaru/next.js,zeit/next.js,flybayer/next.js,flybayer/next.js,flybayer/next.js