Don't display hidden activities over home screen.

Fixes jank exposed in 10881705. Specifically background activity
animating up along with translucent activity. Repro steps on manta:

1. From home start Settings.
2. Press home.
3. From home start Downloads (translucent activity that takes 85% of
screen).
4. Observe that as Downloads zooms up the 15% boundary that should be
dimly transparent are showing Settings.

The cause was that there is a finishing activity in the Downloads task
that was used to launch the DownloadsActivity. The existence of that
activity kept the logic from recognizing that the home activity was
behind the DownloadsActivity, not the Settings activity.

This fix descends through all of the activities in a task sitting on
home and makes sure that they only keep home from showing if such
activities are not finishing and visible.

Change-Id: I607afce6b0000b4db634f2ce40a6c37fcee369d7

1 files changed, 18 insertions, 4 deletions

diff --git a/services/java/com/android/server/am/ActivityStack.java b/services/java/com/android/server/am/ActivityStack.java
index a7fc99593301..4d669461d35d 100644
--- a/services/java/com/android/server/am/ActivityStack.java
+++ b/services/java/com/android/server/am/ActivityStack.java
@@ -1083,10 +1083,24 @@ final class ActivityStack {
                         // At this point, nothing else needs to be shown
                         if (DEBUG_VISBILITY) Slog.v(TAG, "Fullscreen: at " + r);
                         behindFullscreen = true;
-                    } else if (task.mActivities.indexOf(r) == 0 && task.mOnTopOfHome) {
-                        if (DEBUG_VISBILITY) Slog.v(TAG, "Showing home: at " + r);
-                        showHomeBehindStack = true;
-                        behindFullscreen = true;
+                    } else if (task.mOnTopOfHome) {
+                        // Work our way down from r to bottom of task and see if there are any
+                        // visible activities below r.
+                        int rIndex = task.mActivities.indexOf(r);
+                        for ( --rIndex; rIndex >= 0; --rIndex) {
+                            final ActivityRecord blocker = task.mActivities.get(rIndex);
+                            if (!blocker.finishing && blocker.visible) {
+                                if (DEBUG_VISBILITY) Slog.v(TAG, "Home visibility for " +
+                                        r + " blocked by " + blocker);
+                                break;
+                            }
+                        }
+                        if (rIndex < 0) {
+                            // Got to task bottom without finding a visible activity, show home.
+                            if (DEBUG_VISBILITY) Slog.v(TAG, "Showing home: at " + r);
+                            showHomeBehindStack = true;
+                            behindFullscreen = true;
+                        }
                     }
                 } else {
                     if (DEBUG_VISBILITY) Slog.v(