Track polyfill file changes (#9321)

test/.stats-app/stats-config.js

@@ -13,6 +13,10 @@ const clientGlobs = [
       '.next/static/chunks/*.module.js'
     ]
   },
+  {
+    name: 'Legacy Client Bundles (polyfills)',
+    globs: ['.next/static/runtime/+(polyfills)-!(*.module.js)']
+  },
   {
     name: 'Client Pages',
     globs: ['.next/static/*/pages/**/!(*.module.js)']
@@ -44,6 +48,10 @@ const renames = [
     srcGlob: '.next/static/runtime/webpack-!(*.module.js)',
     dest: '.next/static/runtime/webpack-HASH.js'
   },
+  {
+    srcGlob: '.next/static/runtime/polyfills-!(*.module.js)',
+    dest: '.next/static/runtime/polyfills-HASH.js'
+  },
   {
     srcGlob: '.next/static/chunks/commons!(*.module.js)',
     dest: '.next/static/chunks/commons.HASH.js'