AppOps: Prevent deadlock when making note of applications

If noteOperation() is called with ActivityManagerService locked,
AppOpsService won't be able to show the PermissionDialog, causing
noteOperation() to wait indefinitely. Keep a reference to the
current ActivityManagerService instance so that we can check
whether showing the PermissionDialog is safe or not.

Even though there's currently no code path that causes startOperation()
to be called with ActivityManagerService locked, add the same check
there to prevent the same from happening in future.

BUGBASH-17

Change-Id: I118aac6ddf91774a038d73047162cfdb8395e58d