arc: Fix debug crash for start_always mode.

Test: Manually
Bug: N/A
Change-Id: Ic178c9b6b6c512c2720c7c638a7903657c418d99
Reviewed-on: https://chromium-review.googlesource.com/792016Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Commit-Queue: Yury Khmel <khmel@google.com>
Cr-Commit-Position: refs/heads/master@{#519572}

chrome/browser/chromeos/arc/arc_session_manager.h

@@ -308,7 +308,7 @@ class ArcSessionManager : public ArcSessionRunner::Observer,
   void OnBackgroundAndroidManagementChecked(
       policy::AndroidManagementClient::Result result);
 
-  // Requests to starts ARC instance. Also, update the internal state to
+  // Requests to start ARC instance. Also, updates the internal state to
   // ACTIVE.
   void StartArc();
 

chromeos/dbus/session_manager_client.cc

@@ -1031,8 +1031,10 @@ class SessionManagerClientStubImpl : public SessionManagerClient {
                         bool enable_vendor_privileged,
                         bool native_bridge_experiment,
                         StartArcInstanceCallback callback) override {
-    std::move(callback).Run(StartArcInstanceResult::UNKNOWN_ERROR,
-                            std::string(), base::ScopedFD());
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::BindOnce(std::move(callback),
+                                  StartArcInstanceResult::UNKNOWN_ERROR,
+                                  std::string(), base::ScopedFD()));
   }
 
   void SetArcCpuRestriction(