Fix lifecycle bug in when calling positionTask

Sometimes the resumed activity from another stack gets positioned
BELOW the top activity of the current stack. We need to carry over
the mResumedActivity to make sure onPause is called on the moved
activity.

Bug: 28235047
Change-Id: I09e6b032cd8d0b00dc5fdd06bec68e53c25aae73

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

@@ -116,6 +116,7 @@ import android.os.UserHandle;
 import android.service.voice.IVoiceInteractionSession;
 import android.util.ArraySet;
 import android.util.EventLog;
+import android.util.Log;
 import android.util.Slog;
 import android.view.Display;
 
@@ -5025,10 +5026,20 @@ final class ActivityStack {
     }
 
     void positionTask(final TaskRecord task, int position) {
+        final ActivityRecord topRunningActivity = task.topRunningActivityLocked();
+        final boolean wasResumed = topRunningActivity == task.stack.mResumedActivity;
         final ActivityStack prevStack = preAddTask(task, "positionTask");
         task.stack = this;
         insertTaskAtPosition(task, position);
         postAddTask(task, prevStack);
+        if (wasResumed) {
+            if (mResumedActivity != null) {
+                Log.wtf(TAG, "mResumedActivity was already set when moving mResumedActivity from"
+                        + " other stack to this stack mResumedActivity=" + mResumedActivity
+                        + " other mResumedActivity=" + topRunningActivity);
+            }
+            mResumedActivity = topRunningActivity;
+        }
     }
 
     private ActivityStack preAddTask(TaskRecord task, String reason) {