Fix race between WM launching app and AMS freezer

If the next top activity is in cached and frozen mode, WM should raise
its priority to unfreeze it. This is done by calling AMS.updateOomAdj
that will lower its oom adj. However, WM cannot hold the AMS clock
here so the updateOomAdj operation is performed in a separate thread
asynchronously. Therefore WM can't guarantee AMS will unfreeze next top
activity on time. This race will fail the following binder transactions
WM sends to the activity. After this race issue between WM/ATMS and AMS
is solved, this workaround can be removed.

Bug: 213288355
Test: manual stress test, launching all installed apps in a loop
Change-Id: I8ac781ee3faf5711984dab22063083e93217d46e