Exclude the "WebAPK launcher Activity" from recents.

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="{{ version_code }}"
     android:versionName="{{ version_name }}" >
 
     <uses-sdk
         android:minSdkVersion="16"
         android:targetSdkVersion="23" />
 
     <application
         android:icon="@mipmap/app_icon"
         android:label="{{ short_name }}"
         android:allowBackup="false">
         <activity android:name="org.chromium.webapk.shell_apk.MainActivity"
-                  android:theme="@android:style/Theme.Translucent.NoTitleBar">
+                  android:theme="@android:style/Theme.Translucent.NoTitleBar"
+                  android:excludeFromRecents="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
             <intent-filter>
                 <action android:name="android.intent.action.VIEW"></action>
                 <category android:name="android.intent.category.DEFAULT"></category>
                 <category android:name="android.intent.category.BROWSABLE"></category>
                 <data android:scheme="https" android:host="{{ scope_url_host }}" android:pathPrefix="{{ scope_url_path }}"></data>
             </intent-filter>
@@ skipping 41 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>