Build browser app in production mode for performance workflow

Performance measurements might vary drastically in dev vs. production mode.
We are mostly interested in production performance -> update performance workflow
to use browser app in production mode.

Contributed on behalf of ST Microelectronics

.github/workflows/performance.yml

@@ -36,18 +36,27 @@ jobs:
         with:
           repository: eclipse-theia/theia
           path: ./theia
-
+      - name: Copy webpack config
+        shell: bash
+        run: |
+          cp -f ./configs/theia.production.webpack.config.js ./theia/examples/browser/webpack.config.js
       - name: Build Theia
         shell: bash
         working-directory: ./theia
         run: |
           yarn --skip-integrity-check --network-timeout 100000
           yarn download:plugins
-          yarn browser build
         env:
           NODE_OPTIONS: --max_old_space_size=4096
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} # https://github.com/microsoft/vscode-ripgrep/issues/9
-
+      - name: Build Browser App (Production)
+        shell: bash
+        working-directory: ./theia/examples/browser
+        run: |
+          yarn -s compile && yarn rebuild && yarn theia build --mode=production
+        env:
+          NODE_OPTIONS: --max_old_space_size=4096
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} # https://github.com/microsoft/vscode-ripgrep/issues/9
       - name: Run Theia
         shell: bash
         working-directory: ./theia

configs/theia.production.webpack.config.js

@@ -0,0 +1,45 @@
+/**
+ * This file can be edited to customize webpack configuration.
+ * To reset delete this file and rerun theia build again.
+ */
+// @ts-check
+const configs = require('./gen-webpack.config.js');
+const nodeConfig = require('./gen-webpack.node.config.js');
+const TerserPlugin = require('terser-webpack-plugin');
+
+/**
+ * Expose bundled modules on window.theia.moduleName namespace, e.g.
+ * window['theia']['@theia/core/lib/common/uri'].
+ * Such syntax can be used by external code, for instance, for testing.
+ */
+configs[0].module.rules.push({
+    test: /\.js$/,
+    loader: require.resolve('@theia/application-manager/lib/expose-loader')
+});
+
+configs[0].optimization = {
+    minimizer: [
+        new TerserPlugin({
+            terserOptions: {
+                keep_classnames: true
+            }
+        })
+    ]
+};
+
+if (nodeConfig.config.optimization) {
+    nodeConfig.config.optimization.minimizer = [
+        new TerserPlugin({
+            terserOptions: {
+                keep_classnames: true
+            },
+            exclude: /^(lib|builtins)\//
+        })
+    ]
+}
+
+
+module.exports = [
+    ...configs,
+    nodeConfig.config
+];