Save TaskRecord before calling performClearTaskLocked.

If the activity exists in a task that is in persistent storage, the
task reference will be cleared when its brought to the foreground in
this method. Alternatively, if the activity is finished immediately
as a result of clearing task, the task reference will be lost.

Therefore, we must persist the task reference before calling it.

Change-Id: Id38cf6654f5d4f5b727441048dc6b9a7568b574e
Fixes: 35868563
Test: manual (code and bugreport inspection)

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

@@ -1556,9 +1556,13 @@ class ActivityStarter {
                 == (FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TASK)) {
             // The caller has requested to completely replace any existing task with its new
             // activity. Well that should not be too hard...
-            intentActivity.task.performClearTaskLocked();
-            intentActivity.task.setIntent(mStartActivity);
+            // Note: we must persist the {@link TaskRecord} first as intentActivity could be
+            // removed from calling performClearTaskLocked (For example, if it is being brought out
+            // of history or if it is finished immediately), thus disassociating the task.
             mReuseTask = intentActivity.task;
+            mReuseTask.performClearTaskLocked();
+            mReuseTask.setIntent(mStartActivity);
+
             // When we clear the task - focus will be adjusted, which will bring another task
             // to top before we launch the activity we need. This will temporary swap their
             // mTaskToReturnTo values and we don't want to overwrite them accidentally.