Call SetArcCpuRestriction() if StartArc() is called for ARC kiosk

This CL depends on crrev.com/488879. See CL:601768 for more
details.

BUG=b:64327302
TEST=try

Change-Id: I7158787dcb852d84ed78032ea51c97e3dce8cea0
Reviewed-on: https://chromium-review.googlesource.com/601772Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491952}

chrome/browser/chromeos/arc/arc_session_manager.cc

@@ -644,6 +644,10 @@ bool ArcSessionManager::RequestEnableImpl() {
 
   if (start_arc_directly) {
     StartArc();
+    // When in ARC kiosk mode, there's no Chrome tabs to restore. Remove the
+    // cgroups now.
+    if (IsArcKioskMode())
+      SetArcCpuRestriction(false /* do_restrict */);
     // Check Android management in parallel.
     // Note: StartBackgroundAndroidManagementCheck() may call
     // OnBackgroundAndroidManagementChecked() synchronously (or