Fix issue #2329765: Activities are not being immediately stopped.

This was caused by the launchers new hidden surface on top.  The
algorithm for determining whether an activity was visible assumed
that all windows would want to be visible.  Now it ignores ones that
have explicitly requested to be hidden.

services/java/com/android/server/WindowManagerService.java

@@ -8511,7 +8511,8 @@ public class WindowManagerService extends IWindowManager.Stub
             final int N = allAppWindows.size();
             for (int i=0; i<N; i++) {
                 WindowState win = allAppWindows.get(i);
-                if (win == startingWindow || win.mAppFreezing) {
+                if (win == startingWindow || win.mAppFreezing
+                        || win.mViewVisibility != View.VISIBLE) {
                     continue;
                 }
                 if (DEBUG_VISIBILITY) {