arc: Handle default app not availble case.

components/arc/common/app.mojom

Index: components/arc/common/app.mojom
diff --git a/components/arc/common/app.mojom b/components/arc/common/app.mojom
index 6aedc0dacf180e35f341ff4ccd4b2f7f9fbb5004..fa7f0b9b2965b125ea74d06b814d6d7483aba684 100644
--- a/components/arc/common/app.mojom
+++ b/components/arc/common/app.mojom
@@ -2,7 +2,7 @@
 // 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;
 
@@ -129,11 +129,17 @@ interface AppHost {
   // 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 is finished.
-  [MinVersion=16] OnInstallationFinished@15();
+  // 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. |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,