Run OnLaunchedOrRequestExpired on current thread

This change adjusts the call to
ArcAppLaunchThrottleObserver::OnLaunchedOrRequestExpired so that it always runs
in the current thread. This prevents crashes resulting from
SetArcCpuRestriction being called on different thread.

and build/flash/run. Ensure no crashes when a launch request expires.

Bug: 1017211
Test: Test launch request expiration by setting kAppLaunchTimeout to 0
Change-Id: I2430471aa5d69344a879a2c312764d810a03aa55
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879332Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Commit-Queue: Willie Koomson <wvk@google.com>
Auto-Submit: Willie Koomson <wvk@google.com>
Cr-Commit-Position: refs/heads/master@{#709512}

chrome/browser/chromeos/arc/instance_throttle/arc_app_launch_throttle_observer.cc

@@ -46,7 +46,7 @@ void ArcAppLaunchThrottleObserver::OnAppLaunchRequested(
   SetActive(true);
   current_requests_.insert(app_info.package_name);
   base::PostDelayedTask(
-      FROM_HERE,
+      FROM_HERE, {base::CurrentThread()},
       base::BindOnce(&ArcAppLaunchThrottleObserver::OnLaunchedOrRequestExpired,
                      weak_ptr_factory_.GetWeakPtr(), app_info.package_name),
       kAppLaunchTimeout);