Ensure that focusable stack is focused when starting a new activity.

- When starting a new activity, if the old top activity was not
  focusable the focused stack was not updated, leaving the activity
  in a non-resumed state.  Now, ensure that we focus the stack if
  starting an activity allows the stack to be focused.

Test: Enable tap-through in the SystemUI tuner, tap on the activity and
      ensure the menu shows.

Bug: 32636739
Change-Id: I8dd964baacd1e7352880ddd2b2324b947cbec556

services/core/java/com/android/server/am/ActivityStarter.java

@@ -1199,6 +1199,14 @@ class ActivityStarter {
                 // since the app transition will not be triggered through the resume channel.
                 mWindowManager.executeAppTransition();
             } else {
+                // If the target stack was not previously focusable (previous top running activity
+                // on that stack was not visible) then any prior calls to move the stack to the
+                // will not update the focused stack.  If starting the new activity now allows the
+                // task stack to be focusable, then ensure that we now update the focused stack
+                // accordingly.
+                if (mTargetStack.isFocusable() && !mSupervisor.isFocusedStack(mTargetStack)) {
+                    mTargetStack.moveToFront("startActivityUnchecked");
+                }
                 mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity,
                         mOptions);
             }