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]
 enum OrientationLock {
   NONE = 0,
   // Rotated 90 or 270 deg.
   PORTRAIT = 1,
   // Rotated 0 or 180 deg.
   LANDSCAPE = 2,
   // Keep the current orientation.
   CURRENT = 3,
   // Rotated 90 deg.
   PORTRAIT_PRIMARY = 4,
   // Rotated 0 deg.
   LANDSCAPE_PRIMARY = 5,
   // Rotated 270 deg.
   PORTRAIT_SECONDARY = 6,
   // Rotated 180 deg.
   LANDSCAPE_SECONDARY = 7,
 };
 
+// Describes installation result.
+struct InstallationResult {
+  string package_name;
+  bool success;  // true if app was installed successfully.
+};
+
 // Describes ARC app.
 struct AppInfo {
   string name;
   string package_name;
   string activity;
   [MinVersion=2] bool sticky;  // true if the app cannot be uninstalled
   [MinVersion=7] bool notifications_enabled;
   [MinVersion=12] OrientationLock orientation_lock;
 };
 
@@ skipping 78 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);

[dcheng, 2017/01/05 06:54:05]

How come the package name is optional here?

[khmel, 2017/01/05 15:24:29]

My intention here to support versions < 17. If I declare it as required  , as I
understand, in case Android side version is 16, it would be impossible to make
this call.

 
-  // Notifies that Play Store installation is finished.
-  [MinVersion=16] OnInstallationFinished@15();
+  // Notifies that Play Store installation is finished. |result| contains 
+  // details of installation result.
+  [MinVersion=16] OnInstallationFinished@15(
+      [MinVersion=17] InstallationResult? result@1);
 
   // 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);
 };