Close the shell when all activities are destroyed.

shell/android/apk/src/org/chromium/mojo/shell/ShellService.java

 // 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.
 
 package org.chromium.mojo.shell;
 
 import android.app.Activity;
 import android.app.Service;
 import android.content.ComponentName;
 import android.content.Context;
@@ skipping 136 matching lines @@
         return mBinder;
     }
 
     @Override
     public void onTaskRemoved(Intent rootIntent) {
         if (!rootIntent.getComponent().getClassName().equals(ViewportActivity.class.getName())) {
             return;
         }
         String viewportId = rootIntent.getStringExtra("ViewportId");
         NativeViewportSupportApplicationDelegate.viewportClosed(viewportId);
+
+        if (ApplicationStatus.getRunningActivities().size() == 0) {
+            // There are only background apps in the shell, so we close ourselves so we can cleanly
+            // restart. We may want to investigate how to keep backround apps and restart UI
+            // activities cleanly.
+            nativeQuitShell();
+        }
     }
 
     /**
      * Initializes the native system and starts the shell.
      **/
     private void ensureStarted(Context applicationContext, List<String> args) {
         if (mInitialized) return;
         try {
             FileHelper.extractFromAssets(applicationContext, NETWORK_LIBRARY_APP,
                     getLocalAppsDir(applicationContext), false);
@@ skipping 147 matching lines @@
      **/
     private static native void nativeStart(Context context, AssetManager assetManager,
             String mojoShellChildPath, String[] args, String bundledAppsDirectory, String tmpDir,
             String homeDir);
 
     private static native void nativeAddApplicationURL(String url);
 
     private static native void nativeStartApplicationURL(String url);
 
     private static native void nativeBindShell(int shellHandle);
+
+    private static native void nativeQuitShell();
 }