separate webpack runtime into its own chunk to maintain cacheability of common chunk

app/views/layouts/_head.html.haml

@@ -28,6 +28,7 @@
   = stylesheet_link_tag "application", media: "all"
   = stylesheet_link_tag "print",       media: "print"
+  = javascript_include_tag(*webpack_asset_paths("manifest"))
   = javascript_include_tag(*webpack_asset_paths("common"))
   = javascript_include_tag(*webpack_asset_paths("application"))

config/webpack.config.js

@@ -98,10 +98,9 @@ var config = {
       new webpack.HashedModuleIdsPlugin() :
       new webpack.NamedModulesPlugin(),
-    // create a common.js bundle to be loaded on every page
+    // create cacheable common library bundles
     new webpack.optimize.CommonsChunkPlugin({
-      name: 'common',
-      minChunks: Infinity,
+      names: ['application', 'common', 'manifest'],
     }),
   ],