Lazily instantiate the TextEncoder in platform_browser (#2032)
Lazily instantiate the TextEncoder in platform_browser (#2032)

BUG

This makes browsers that don't support TextEncoders fail later only when encoding happens (which typically is rare).
tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs