Don't remove task needed for reuse when clearing during activity start.

Bug: 26541093
Change-Id: I4ed39110e9bd72e5f7e11a49acc0a36dc8414df4
diff --git a/services/core/java/com/android/server/am/TaskRecord.java b/services/core/java/com/android/server/am/TaskRecord.java
index c6444bf..71cfeab 100644
--- a/services/core/java/com/android/server/am/TaskRecord.java
+++ b/services/core/java/com/android/server/am/TaskRecord.java
@@ -206,7 +206,7 @@
 
     // Used in the unique case where we are clearing the task in order to reuse it. In that case we
     // do not want to delete the stack when the task goes empty.
-    boolean mReuseTask = false;
+    private boolean mReuseTask = false;
 
     private Bitmap mLastThumbnail; // Last thumbnail captured for this item.
     private final File mLastThumbnailFile; // File containing last thumbnail.
@@ -777,6 +777,13 @@
         mReuseTask = false;
     }
 
+    ActivityRecord performClearTaskForReuseLocked(ActivityRecord newR, int launchFlags) {
+        mReuseTask = true;
+        final ActivityRecord result = performClearTaskLocked(newR, launchFlags);
+        mReuseTask = false;
+        return result;
+    }
+
     /**
      * Perform clear operation as requested by
      * {@link Intent#FLAG_ACTIVITY_CLEAR_TOP}: search from the top of the