Update android SDK to API version 23.

shell/android/apk/AndroidManifest.xml.jinja2

 <?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="{{ manifest_package }}"
@@ skipping 12 matching lines @@
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
 
     <application android:icon="@mipmap/ic_launcher"
             android:name="org.chromium.mojo.shell.MojoShellApplication"
             android:label="{{ apk_name }}">
         <meta-data android:name="com.google.android.gms.version"
                    android:value="@integer/google_play_services_version" />
         <activity android:name="org.chromium.mojo.shell.MojoShellActivity"
                   android:launchMode="standard"
                   android:documentLaunchMode="none"
-                  android:theme="@android:style/Theme.NoDisplay">
+                  android:theme="@style/Theme.Transparent">
             <intent-filter>
                 <!-- A mojo://host/path url will load the app at the
                      https://host/path URL.
                  -->
                 <data android:scheme="mojo"/>
                 <action android:name="android.intent.action.VIEW"/>
                 <category android:name="android.intent.category.DEFAULT"/>
                 <category android:name="android.intent.category.BROWSABLE"/>
             </intent-filter>
         </activity>
@@ skipping 20 matching lines @@
                 <data android:mimeType="text/plain"/>
             </intent-filter>
         </activity>
         <activity android:name="org.chromium.mojo.shell.IntentReceiverActivity"
                   android:theme="@style/Theme.Transparent">
         </activity>
         <service android:name="org.chromium.mojo.shell.ShellService" />
     </application>
 
 </manifest>