Avoid race condition with hotseat predictions.

Make sure that the ArrayList cannot be cleared on the model thread while
it is being used on the UI thread to render a launcher preview.

Test: Manual
Fix: 210123588
Change-Id: I5a47cb3f28f5ac9e400f6ae535e410c345e14ee1

quickstep/src/com/android/launcher3/model/WidgetsPredictionUpdateTask.java

@@ -59,8 +59,8 @@ public final class WidgetsPredictionUpdateTask extends BaseModelUpdateTask {
         Map<PackageUserKey, List<WidgetItem>> allWidgets =
                 dataModel.widgetsModel.getAllWidgetsWithoutShortcuts();
 
-        FixedContainerItems fixedContainerItems = mPredictorState.items;
-        fixedContainerItems.items.clear();
+        FixedContainerItems fixedContainerItems =
+                new FixedContainerItems(mPredictorState.containerId);
 
         if (FeatureFlags.ENABLE_LOCAL_RECOMMENDED_WIDGETS_FILTER.get()) {
             for (AppTarget app : mTargets) {
@@ -100,6 +100,7 @@ public final class WidgetsPredictionUpdateTask extends BaseModelUpdateTask {
                 }
             }
         }
+        dataModel.extraItems.put(mPredictorState.containerId, fixedContainerItems);
         bindExtraContainerItems(fixedContainerItems);
 
         // Don't store widgets prediction to disk because it is not used frequently.