[WebViewShell] retarget the shell to N for testing.

android_webview/tools/system_webview_shell/apk/AndroidManifest.xml

 <!--
  * 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"
     package="org.chromium.webview_shell"
     android:versionCode="1"
     android:versionName="1.0" >
 
-    <uses-sdk android:minSdkVersion="19" android:targetSdkVersion="23" />
+    <uses-sdk android:minSdkVersion="19" android:targetSdkVersion="24" />
 
     <!-- "Normal" permissions which do not require user prompt -->
     <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
     <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
     <uses-permission android:name="android.permission.INTERNET" />
     <uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS"/>
     <uses-permission android:name="android.permission.USE_CREDENTIALS"/>
 
     <!-- "Dangerous" permissions which require user prompt -->
     <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
@@ skipping 74 matching lines @@
 
         <activity
             android:name="org.chromium.webview_shell.PageCyclerTestActivity"
             android:label="@string/title_activity_page_cycler"
             android:exported="true">
         </activity>
 
         <uses-library android:name="android.test.runner" />
     </application>
 </manifest>