[browserstack benchmark tool] Add a html to present benchmark results

[Linchenn]

For browserstack benchmark tool, when you run:
node app.js --benchmark='./preconfigured_browser.json' --cloud --outfile, the program will benchmark all models on devices configured in preconfigured_browser.json file and then write down the benchmark results into a json file benchmark_results.json, which is too large to be readable.

This PR:

1. lets the program write the benchmark results into a javascript variable (in benchmark_results.js), instead of a json file (benchmark_results.json). Then the benchmark results could be loaded easily to the html file.
2. add a html file, which loads benchmark_results.js and renders the benchmark results into a table.

Then, whenever complete node app.js --benchmark='./preconfigured_browser.json' --cloud --outfile, users no longer need to read benchmark_results.json, and, they could simply open benchmark_results.html to see the results.

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This change is 

(For developers only: if want to use typescript to re-write this, could continue on #6741)

[lina128]

LGTM

[pyu10055]

Thanks, can you allow either json or html to be generated?
maybe use a command line flag?

Reviewable status: complete! 1 of 1 approvals obtained

[Linchenn]

Great catch!
Updated outfile argument. Thank you!

Reviewable status: complete! 1 of 1 approvals obtained

[pyu10055]

awesome, thanks

Reviewed 1 of 2 files at r2, 1 of 2 files at r4, 2 of 2 files at r5, all commit messages.
Reviewable status: complete! 2 of 1 approvals obtained