Move most or all of chipper-startup.js to a preload

[samreid]

From #764

I said:

(8) Is there a way to get (almost all of) chipper-startup.js to run as a standard preload, referenced from chipper/build.json? That would help unify this new code with existing code, and get rid of the code like this:

  const startupJS = grunt.file.read( '../chipper/templates/chipper-startup.js' );
  const productionStartupJS = minify( startupJS, minifyOptions );
  const debugStartupJS = minify( startupJS, debugMinifyOptions );

Moving toward this strategy may help us reach the goal of running this new code in requirejs + built mode?

[samreid]

@jonathanolson replied:

There is definitely opportunity for simplification (I'm including some cleanup in the above commit). We independently minify the four of these in both production and debug ways: ...productionPreloads, productionStringsJS, productionJS, productionStartupJS. The strings JS (chipper-strings.js) is only for built mode, as we have a different way of loading strings in require.js, so I don't feel like there is a fully unified approach.

[samreid]

This seems related to #769. I agree that custom logic is needed for productionPreloads, productionStringsJS, productionJS, productionStartupJS, but I'm not seeing why (almost all?) of chipper-startup.js shouldn't be in a preload. What are the drawbacks of making it a standard preload? Can this be investigated further?

[samreid]

@jonathanolson also said in slack:

Scenery itself (and standalone builds) don’t have preloads, so it would take some larger architectural build challenges to get that to work (but that I could look into)

[jonathanolson]

So I realized that Scenery won't need chipper-startup, so I believe we can ignore my previous comment!

It's possible to rewrite sim-development.html so that it calls loadURL on chipper-startup.js, however it's important to note that this CANNOT be a "preload" in general, because in the built form, it needs to be run AFTER the require.js script is executed, and would be more of a "postload".

[jonathanolson]

The branch above has a commit that has the require.js startup mode also use chipper-startup.js. @samreid what are your thoughts on it? Commit is f30b263

[samreid]

The change set looks great and works nicely, but I noticed around a 120ms delay in the startup time using this patch. This is a short amount of time, but it's longer than I expected. I still think we should proceed with this, but was surprised by the 120ms and wanted to run it past you.

UPDATE: to clarify, I measured this time by putting Date.now() right before loading chipper-startup.js and right at the beginning of the runRequireJS callback.