The filename options used by babylon is called `sourceFilename` and not `filename`. Therefore the option should be adjusted to be called `sourceFilename`.
* Flip default parameter template
YMMV, I saved ~10b on a 2kb library. Not noticeable at the small scale, by why not do it anyway?
I've (unscientifically) found that flipping the default parameter conditional yields better gzip results. I think this is due to the slightly longer string it can now repeatedly match:
```js
// old
var param = arguments.length <= 0 || void 0 === arguments[0] ? null : arguments[0]
--------------------------------------------------------------^
// new
var param = arguments.length > 1 && void 0 !== arguments[1] ? arguments[1] : null
------------------------------------------------------------------------^
```
Though it's entirely likely gzip will also choose up to the index of the arguments if you many default parameters at different indexes.
* Update tests
* Removed unnecessary 'return' statements.
Returning a 'Promise' value in 'promise.then()' makes promise chains.
Used memory and promises are not garbage collected
until finishing 'helpers.asyncToGenerator'.
* Update test
* Fix class inheritance in IE9 & IE10 (T3041)
Internet Explorer 9&10 do not support __proto__ at all, don't have
Object.setPrototypeOf(), but have Object.getPrototypeOf().
Because of this setting the prototype is not possible, which makes the
babelHelpers.inherits() function to set __proto__ although not supported.
Afterwards Object.getPrototypeOf() is used, but this one is not
respecting the "custom" property __proto__ that we set.
The solution is to check for __proto__ first and afterwards fallback to
Object.getPrototypeOf().
* Do the same logic in babel-helper-replace-supers
* Fix tests
* Extract creation of prototype nodes to small helper
This reverts commit 033681af8941d9678961f985c13e500c3c70f337, reversing
changes made to a2d66c0fc8ee58e82be3efd59173803e66dee3e0.
I brought you into this world, and I can take you out.
`build-config-chain.js` creates an array of options which will be passed to `OptionsManager#mergeOptions`. The advantage of separating it out is that `build-config-chain` has a very minimal dependency list. The eventual intent is to allow the require hook to lazy load only when required. In other words, if no required files ever match the patterns `ignore` / `only` patterns, the bulk of babel-core, and the associated plugins, will never be loaded.
