PERF: Concatenate scripts in development mode

This improves my DOMContentLoaded from 9s+ to less than 4s.
Pinging @SamSaffron on this because this was previously controversial.

This implementation adds the `@sourceURL` directive so chrome correctly
identifies the source files.

config/environments/development.rb

@@ -22,7 +22,7 @@ Discourse::Application.configure do
   # Don't Digest assets, makes debugging uglier
   config.assets.digest = false
 
-  config.assets.debug = true
+  config.assets.debug = false
 
   # Raise an error on page load if there are pending migrations
   config.active_record.migration_error = :page_load

lib/discourse_iife.rb

@@ -32,6 +32,7 @@ class DiscourseIIFE < Sprockets::Processor
                      .sub("/app/assets/javascripts", "")
                      .sub("/test/javascripts", "")
       res << "\nwindow.__jshintSrc = window.__jshintSrc || {}; window.__jshintSrc['/assets#{req_path}'] = #{data.to_json};\n"
+      res << "\n//@ sourceURL=/#{context.logical_path}\n"
     end
 
     res

lib/es6_module_transpiler/tilt/es6_module_transpiler_template.rb

@@ -127,6 +127,7 @@ module Tilt
         req_path = "/assets/#{scope.logical_path}.#{extension}"
 
         @output << "\nwindow.__jshintSrc = window.__jshintSrc || {}; window.__jshintSrc['#{req_path}'] = #{data.to_json};\n"
+        @output << "\n//@ sourceURL=/#{scope.logical_path}\n"
       end
 
       @output