Reduce build size by 33%

[ebidel]

R: all

In this spirit of #1690, I've managed to get the build down to 1.6MB. 33% savings!

Other low hanging fruit is stripping out the html/js license comments in the inlined files (readFileSync).

This PR introduces uglify-harmony into the extension gulpfile. gulp build:production will build lighthouse-extension.js and also compress it. gulp build continues to only broswerify. I felt that we may still want to keep that around for speedlier development when making tweaks to the crx. Happy to consolidate though.

[patrickhulce]

Interesting how does this disrupt array notation specifically? I had thought mangle was fine unless Function.name/with/eval though I'm not familiar with uglify-harmony gotchas

[ebidel]

It's pretty tricky to track down where things break down, but without mangle: false, the audit names get rewritten:

Hard to say if it also creates other errors.

[patrickhulce]

Oh right because we do use Function.name there with the gatherer class name, maybe update that comment then? The accessors seems like the secondary issue to the primary problem of the gatherer being renamed :)

[paulirish]

In build-traceviewer-module.js we use babel to do some lightweight minification:

lighthouse/lighthouse-core/scripts/build-traceviewer-module.js

Lines 134 to 138 in 7a5448e

	transformed = babel.transform(transformed, {
	plugins: ['transform-es2015-destructuring'],
	comments: false, // Output comments in generated output.
	compact: true // Do not include superfluous whitespace characters and line terminators.
	}).code;

are you open to using that? this way we wouldn't have to deal with disabling a bunch of options like mangle and sideEffects.

[ebidel]

For the life of me, I couldn't get babel, typescript, or closure to play nicely.

• Closure - I wanted closure because it produces the smallest output, but it is really slow on 2.4MB of JS and does not support a non-transpiled option.
• Babel - https://github.com/babel/babili looked the most promising (to avoid transpilation) but it choked after a certain amount of code and stopped minifying it.
• Typescript - removes comments but does not minify.

In terms of filesize reduction, I didn't find disabling a few compressor settings to adversely effect file size that much.

[XhmikosR]

Isn't dead code supposed to be caught by ESLint?

[ebidel]

Even if it does, we're not running eslint over the browserified bundle.

[paulirish]

I put up #1765 which replaces uglify with babel. It has one benefit of not adding any new dependencies at all. :)