arc: Handle default app not availble case.

components/arc/common/app.mojom

 // 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.
 //
-// Next MinVersion: 17
+// Next MinVersion: 18
 
 module arc.mojom;
 
 import "scale_factor.mojom";
 import "screen_rect.mojom";
 
 // Describes OrientationLock request.
 // Note: ChromeOS currently assumes the internal panel is always landscape.
 // All rotation angles mentioned here are measured clockwise.
 [Extensible]
@@ skipping 106 matching lines @@
   // Notifies that task has been activated.
   [MinVersion=4] OnTaskSetActive@6(int32 task_id);
 
   // Notifies that notifications enabled settings in Android is changed.
   [MinVersion=7] OnNotificationsEnabledChanged@7(string package_name,
                                                  bool enabled);
 
   // Notifies that an application shortcut needs to be created.
   [MinVersion=9] OnInstallShortcut@11(ShortcutInfo shortcut);
 
-  // Notifies that Play Store installation has been started.
-  [MinVersion=16] OnInstallationStarted@14();
+  // Notifies that Play Store installation has been started. |package_name|
+  // specifies installation package
+  [MinVersion=16] OnInstallationStarted@14(
+      [MinVersion=17] string? package_name@0);
 
-  // Notifies that Play Store installation is finished.
-  [MinVersion=16] OnInstallationFinished@15();
+  // Notifies that Play Store installation is finished. |package_name| specifies
+  // installation package and |success| contains true if installation has
+  // completed successfully.
+  [MinVersion=16] OnInstallationFinished@15(
+      [MinVersion=17] string? package_name@0,
+      [MinVersion=17] bool success@1);

[Luis Héctor Chávez, 2017/01/03 19:08:00]

doesn't this also need to be optional? otherwise you'll get 'false' as the
default value instead of OptionNone.

[khmel, 2017/01/03 21:40:56]

Bool cannot be optional. So I embedded everything to struct

 
   // Notifies that task requested orientation lock.
   [MinVersion=12] OnTaskOrientationLockRequested@12(int32 task_id,
                                                     OrientationLock lock);
 };
 
 // TODO(lhchavez): Migrate all request/response messages to Mojo.
 // Next method ID: 16
 // Deprecated method ID: 9
 interface AppInstance {
@@ skipping 60 matching lines @@
                                            ShowPackageInfoPage page,
                                            ScreenRect dimension_on_screen);
 
   // Sets notification setting for the package.
   [MinVersion=6] SetNotificationsEnabled@10(string package_name, bool enabled);
 
   // Sends a request to ARC to uninstall the given package.  Error (if ever
   // happens) is ignored, and uninstall option should appear in the UI.
   [MinVersion=2] UninstallPackage@5(string package_name);
 };