Fix returning an occluded activity below boundary

WindowContainer#getActivity() was returning null if there was no
matching activity or hit the boundary. Since we were unable to
tell the difference between the two cases, we would continue looking
for a matching activity from higher level window containers.

Take below hierarchy for example, #getActivity() returns null if
the boundary was TopActivity. So, we were kept looking for the matching
activity from Task#2 and returns BottomActivity.

RootTask
  - Task#1
     - TopActivity
  - Task#2
     - BottomActivity

Bug: 156014697
Test: start activity from recents in split-secondary
Change-Id: Ic344e8c1c47e9fa05c4de60be8c6b30f75cdb0bc

services/core/java/com/android/server/wm/ActivityRecord.java

@@ -3589,7 +3589,7 @@ final class ActivityRecord extends WindowToken implements WindowManagerService.A
 
     @Override
     ActivityRecord getActivity(Predicate<ActivityRecord> callback, boolean traverseTopToBottom,
-            WindowContainer boundary) {
+            ActivityRecord boundary) {
         return callback.test(this) ? this : null;
     }
 

services/core/java/com/android/server/wm/ActivityStack.java

@@ -2689,7 +2689,9 @@ class ActivityStack extends Task {
      */
     @Nullable
     private ActivityRecord getOccludingActivityAbove(ActivityRecord activity) {
-        return getActivity((ar) -> ar.occludesParent(), true /* traverseTopToBottom */, activity);
+        ActivityRecord top = getActivity((ar) -> ar.occludesParent(),
+                true /* traverseTopToBottom */, activity);
+        return top != activity ? top : null;
     }
 
     boolean willActivityBeVisible(IBinder token) {

services/core/java/com/android/server/wm/WindowContainer.java

@@ -1415,11 +1415,12 @@ class WindowContainer<E extends WindowContainer> extends ConfigurationContainer<
     }
 
     ActivityRecord getActivity(Predicate<ActivityRecord> callback, boolean traverseTopToBottom,
-            WindowContainer boundary) {
+            ActivityRecord boundary) {
         if (traverseTopToBottom) {
             for (int i = mChildren.size() - 1; i >= 0; --i) {
                 final WindowContainer wc = mChildren.get(i);
-                if (wc == boundary) return null;
+                // TODO(b/156986561): Improve the correctness of the boundary check.
+                if (wc == boundary) return boundary;
 
                 final ActivityRecord r = wc.getActivity(callback, traverseTopToBottom, boundary);
                 if (r != null) {
@@ -1430,7 +1431,8 @@ class WindowContainer<E extends WindowContainer> extends ConfigurationContainer<
             final int count = mChildren.size();
             for (int i = 0; i < count; i++) {
                 final WindowContainer wc = mChildren.get(i);
-                if (wc == boundary) return null;
+                // TODO(b/156986561): Improve the correctness of the boundary check.
+                if (wc == boundary) return boundary;
 
                 final ActivityRecord r = wc.getActivity(callback, traverseTopToBottom, boundary);
                 if (r != null) {