Update targetSdkVersion to 23.

chrome/test/chromedriver/test/webview_shell/java/AndroidManifest.xml

 <?xml version="1.0" encoding="utf-8"?>
 
 <!-- Copyright 2013 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.chromedriver_webview_shell" android:versionCode="1"
     android:versionName="1.0">
 
-    <uses-sdk android:minSdkVersion="19" android:targetSdkVersion="21" />
+    <uses-sdk android:minSdkVersion="19" android:targetSdkVersion="23" />
     <uses-permission android:name="android.permission.INTERNET" />
     <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
 
     <application android:label="ChromeDriverWebviewShell"
         android:icon="@drawable/icon"
         android:allowBackup="false">
         <activity android:name=".Main"
             android:launchMode="singleTask"
             android:process=":main"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
     </application>
 
 </manifest>