Differentiate empty UI from default in recents Go

Use the "empty" drawable as the initial UI until the recents task list
and order is loaded, then switch to default/filled UI.

Bug: 114136250
Test: Manual test; see empty UI when loading takes time
Change-Id: I85b72e6d40d7224b28217cbf4e05515ec1e9451b
(cherry picked from commit a2c4200cde475cd5ab9de35945e2e8458589c39c)
diff --git a/go/quickstep/src/com/android/quickstep/TaskHolder.java b/go/quickstep/src/com/android/quickstep/TaskHolder.java
index 91a3534..a3fa5c1 100644
--- a/go/quickstep/src/com/android/quickstep/TaskHolder.java
+++ b/go/quickstep/src/com/android/quickstep/TaskHolder.java
@@ -73,10 +73,7 @@
      */
     public void bindEmptyUi() {
         mTask = null;
-        // TODO: Set the task view to a loading, empty UI.
-        // Temporarily using the one below for visual confirmation but should be swapped out to new
-        // UI later.
-        mTaskItemView.resetTaskItemView();
+        mTaskItemView.resetToEmptyUi();
     }
 
     /**
diff --git a/go/quickstep/src/com/android/quickstep/views/TaskItemView.java b/go/quickstep/src/com/android/quickstep/views/TaskItemView.java
index a8fc78a..572747b 100644
--- a/go/quickstep/src/com/android/quickstep/views/TaskItemView.java
+++ b/go/quickstep/src/com/android/quickstep/views/TaskItemView.java
@@ -37,6 +37,7 @@
  */
 public final class TaskItemView extends LinearLayout {
 
+    private static final String EMPTY_LABEL = "";
     private static final String DEFAULT_LABEL = "...";
     private final Drawable mDefaultIcon;
     private final Drawable mDefaultThumbnail;
@@ -83,17 +84,17 @@
         mThumbnailView.setImageDrawable(mThumbnailDrawable);
         mIconView.setImageDrawable(mIconDrawable);
 
-        resetTaskItemView();
+        resetToEmptyUi();
         CONTENT_TRANSITION_PROGRESS.setValue(this, 1.0f);
     }
 
     /**
-     * Resets task item view to default values.
+     * Resets task item view to empty, loading UI.
      */
-    public void resetTaskItemView() {
-        setLabel(DEFAULT_LABEL);
-        setIcon(null);
-        setThumbnail(null);
+    public void resetToEmptyUi() {
+        mIconDrawable.resetDrawable();
+        mThumbnailDrawable.resetDrawable();
+        setLabel(EMPTY_LABEL);
     }
 
     /**