[mobilent] Add timing number without image extraction and preprocessing (#254)
[mobilent] Add timing number without image extraction and preprocessing (#254)

It turns out that image extraction and preprocessing takes a big fraction of the time.

A typical result (with the new code) looks like:
Done in 76 ms (not including image preprocessing: 21 ms)

tensorflow/tfjs-examples,tensorflow/tfjs-examples,tensorflow/tfjs-examples,tensorflow/tfjs-examples,tensorflow/tfjs-examples,tensorflow/tfjs-examples,tensorflow/tfjs-examples