dart2js: reduce unminified names in .js files

[rakudrama]

There are some common unminified properties in minified code.

Quick analysis of potential savings of an Angular2 + Dart app (compiled with --fast-startup)

Minify $requiredArgCount, $defaultValues, $signature: 1.64%
Minify inherit and installTearOff: 1.66%

Replace most common $signature with references to shared function: 1.5%
171 $signature:function(){return{func:1,args:[,,]}}
180 $signature:function(){return{func:1}}
415 $signature:function(){return{func:1,args:[,]}}

Replace most common $defaultValues:function(){return[]} with reference to shared function: 0.62%

Hopefully references to a shared function would parse faster than functions.

That is 3.3% with simply minifying helper function names and 5.4% with some other simple tricks.
I don't expect that the gzipped file will be smaller.
Subtract 1.66% for the standard emitter.

[joseluis]

I was just going to open an issue about this. There do seems to be still a lot of room for minification.

I'm currently using UglifyJS to further minify the JavaScript code already minified with dart2js, and reducing its size by an additional 10%.

You can see an example comparison here:
https://gist.github.com/joseluis/e2c3c21d72e411d78d6d

• dart2js minified : 112641 bytes
• dart2js minified + uglified: 102947 bytes

[rakudrama]

Additional thing: the static: property is not minified.

[rakudrama]

These changes help with some of the --fast-startup issues:
cdba92a - shares $defaultValues via common base class
0c83262 - shorter names for $requiredArgCount, $defaultValues, $signature.

Still to do:

• "call*" is not yet minified.
• $signature reduced to $S but the repeated functions are not shared.
• It might be possible, through tracing, to eliminate many $signature entries, even when types are needed because of .runtimeType.