Add web_manifest_url in WebappInfo.

chrome/android/webapk/shell_apk/AndroidManifest.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2015 The Chromium Authors. All rights reserved.
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file.
 -->
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
     package="{{ manifest_package }}"
     android:versionCode="1"
     android:versionName="1.0" >
@@ skipping 21 matching lines @@
         </activity>
         <meta-data android:name="runtimeHost" android:value="{{ runtime_host }}" />
         <meta-data android:name="startUrl" android:value="{{ start_url }}" />
         <meta-data android:name="name" android:value="{{ name }}" />
         <meta-data android:name="scope" android:value="{{ scope_url }}" />
         <meta-data android:name="displayMode" android:value="{{ display_mode }}" />
         <meta-data android:name="orientation" android:value="{{ orientation }}" />
         <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"
             tools:ignore="ExportedService">
             <intent-filter>
               <action android:name="android.intent.action.MAIN" />
               <category android:name="android.intent.category.WEBAPK_API" />
             </intent-filter>
         </service>
         <meta-data android:name="org.chromium.content.browser.NUM_SANDBOXED_SERVICES"
@@ skipping 10 matching lines @@
             android:process=":webapk_sandboxed_process1"
             android:exported="true"
             tools:ignore="ExportedService"/>
         <service android:name="org.chromium.webapk.shell_apk.WebApkSandboxedProcessService2"
             android:isolatedProcess="true"
             android:process=":webapk_sandboxed_process2"
             android:exported="true"
             tools:ignore="ExportedService"/>
     </application>
 </manifest>