Add web_manifest_url in WebappInfo.

chrome/android/webapk/shell_apk/AndroidManifest.xml

Index: chrome/android/webapk/shell_apk/AndroidManifest.xml
diff --git a/chrome/android/webapk/shell_apk/AndroidManifest.xml b/chrome/android/webapk/shell_apk/AndroidManifest.xml
index bee919afe6238cde93e6416f3ce145233798f381..14e2062a22b78c210471d1e2f8aefc7b187fed90 100644
--- a/chrome/android/webapk/shell_apk/AndroidManifest.xml
+++ b/chrome/android/webapk/shell_apk/AndroidManifest.xml
@@ -39,6 +39,7 @@
         <meta-data android:name="themeColor" android:value="{{ theme_color }}" />
         <meta-data android:name="backgroundColor" android:value="{{ background_color }}" />
         <meta-data android:name="iconUrl" android:value="{{ icon_url }}" />
+        <meta-data android:name="webManifestUrl" android:value="{{ web_manifest_url }}" />
         <service
             android:name="org.chromium.webapk.shell_apk.WebApkServiceFactory"
             android:exported="true"