Simplify caller checking logic in WebApkServiceImpl

chrome/android/javatests/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. -->
 
 <!-- package name must be unique. -->
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="org.chromium.chrome.tests">
 
     <uses-sdk android:minSdkVersion="16" android:targetSdkVersion="23" />
@@ skipping 41 matching lines @@
 
         <activity android:name="org.chromium.test.broker.OnDeviceInstrumentationBroker"
             android:exported="true"/>
         <!--suppress ExportedReceiver -->
         <receiver android:name="org.chromium.chrome.browser.customtabs.CustomTabsActivityTest$DummyBroadcastReceiver">
             <intent-filter>
                 <action android:name="org.chromium.chrome.browser.customtabs.TEST_PENDING_INTENT_SENT" >
                 </action>
             </intent-filter>
         </receiver>
+
+        <service android:name="org.chromium.chrome.test.webapk.TestWebApkServiceImplWrapper"
+            android:exported="true">
+        </service>
     </application>
 
     <instrumentation android:name="org.chromium.chrome.test.ChromeInstrumentationTestRunner"
         android:targetPackage="{{manifest_package}}"
         android:label="Tests for {{manifest_package}}"/>
 </manifest>