Add an about:flag to control WebApk enablement.

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 9188c195bbacb344c326adcb21e2255b2497d002..51a8175e4ac31eeb261328cc59b27d6dc4db6481 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -14974,6 +14974,14 @@ Please check your email at <ph name="ACCOUNT_EMAIL">$2<ex>jane.doe@gmail.com</ex
       <message name="IDS_FLAGS_TAB_SWITCHER_IN_DOCUMENT_MODE_DESCRIPTION" desc="Description for the flag to enable tab switcher in document mode.">
         If enabled, a tab switcher will show even when 'merge tabs and apps' option is on in the settings.
       </message>
+
+      <!-- WebApks -->
+      <message name="IDS_FLAGS_ENABLE_WEBAPK" desc="Name for the flag to enable WebAPK feature.">
+        Enable WebAPKs
+      </message>
+      <message name="IDS_FLAGS_ENABLE_WEBAPK_DESCRIPTION" desc="Description for the flag to enable WebAPK feature.">
+        Enables packaging PWAs into an Android WebAPK. Requires sending data to a chrome server to generate the application.
+      </message>
     </if>
 
     <message name="IDS_FLAGS_ENABLE_BROTLI_NAME" desc="Title for the flag to enable Brotli Content-Encoding.">