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

Bug: 26541093
Change-Id: I4ed39110e9bd72e5f7e11a49acc0a36dc8414df4

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

@@ -876,7 +876,7 @@ class ActivityStarter {
                 // In this situation we want to remove all activities from the task up to the one
                 // being started. In most cases this means we are resetting the task to its initial
                 // state.
-                final ActivityRecord top = intentActivity.task.performClearTaskLocked(
+                final ActivityRecord top = intentActivity.task.performClearTaskForReuseLocked(
                         mStartActivity, mLaunchFlags);
                 if (top != null) {
                     if (top.frontOfTask) {

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

@@ -206,7 +206,7 @@ final class TaskRecord {
 
     // 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 @@ final class TaskRecord {
         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