add some profiling

and es6 module crosspiler is not slow!!!

lib/js.js

@@ -4,6 +4,7 @@ var recast = lazy('recast')
 var uglify = lazy('uglify-js')
 var esprima = lazy('esprima')
 var debug = require('debug')('ecstacy:js')
+var profile = require('debug')('ecstacy:js:profile')
 var convert = require('convert-source-map')
 var applySourceMap = require('apply-source-map')
 var db = require('polyfills-db').recast
@@ -62,16 +63,20 @@ JS.prototype.minify = function (name) {
 
 JS.prototype._recast = function (code, map, transforms) {
   // i wish there was a way to cache this
+  profile('recasting AST')
   var ast = recast().parse(code, {
     esprima: esprima(),
     sourceFileName: this.name + '.js'
   })
+  profile('recasted AST')
   transforms.forEach(function (transform) {
     ast = transform.transform(ast)
+    profile('performed transform "%s"', transform.name)
   })
   var result = recast().print(ast, {
     sourceMapName: this.name + '.js'
   })
+  profile('stringified AST')
   return {
     code: convert.removeMapFileComments(result.code),
     map: map