Extract the version extract from webpack config (#5798)

build-scripts/env.js

@@ -1,3 +1,7 @@
+const fs = require("fs");
+const path = require("path");
+const paths = require("./paths.js");
+
 module.exports = {
   isProdBuild() {
     return process.env.NODE_ENV === "production";
@@ -11,4 +15,13 @@ module.exports = {
   isNetlify() {
     return process.env.NETLIFY === "true";
   },
+  version() {
+    const version = fs
+      .readFileSync(path.resolve(paths.polymer_dir, "setup.py"), "utf8")
+      .match(/\d{8}\.\d+/);
+    if (!version) {
+      throw Error("Version not found");
+    }
+    return version[0];
+  },
 };