Add flag to WebView apks specifying that these apks contain WebView.

android_webview/apk/java/AndroidManifest.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!--
   Copyright (c) 2012 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"
     package="{{package|default('com.android.webview')}}">
     <uses-sdk android:minSdkVersion="{{minsdk|default(21)}}"
@@ skipping 12 matching lines @@
             <intent-filter>
                 <action android:name="android.settings.WEBVIEW_LICENSE" />
                 <category android:name="android.intent.category.DEFAULT" />
             </intent-filter>
             <meta-data android:name="com.android.settings.PRIMARY_PROFILE_CONTROLLED"
                        android:value="true" />
         </activity>
         <provider android:name="com.android.webview.chromium.LicenseContentProvider"
                   android:exported="true"
                   android:authorities="com.android.webview.chromium.LicenseContentProvider" />
+        <meta-data android:name="com.android.webview.WebViewLibrary"
+                   android:value="libwebviewchromium.so" />
     </application>
 </manifest>