Skip scroll-to animation when undocking and there are no tasks.

Bug: 28367678
Change-Id: Iafd064196cae43f60ff6d356843d1e431d15daea

packages/SystemUI/src/com/android/systemui/recents/RecentsActivity.java

@@ -451,11 +451,13 @@ public class RecentsActivity extends Activity implements ViewTreeObserver.OnPreD
 
         TaskStack stack = loadPlan.getTaskStack();
         int numStackTasks = stack.getStackTaskCount();
+        boolean showDeferredAnimation = numStackTasks > 0;
 
         EventBus.getDefault().send(new ConfigurationChangedEvent(true /* fromMultiWindow */,
                 false /* fromDeviceOrientationChange */, false /* fromDisplayDensityChange */,
                 numStackTasks > 0));
-        EventBus.getDefault().send(new MultiWindowStateChangedEvent(isInMultiWindowMode, stack));
+        EventBus.getDefault().send(new MultiWindowStateChangedEvent(isInMultiWindowMode,
+                showDeferredAnimation, stack));
     }
 
     @Override

packages/SystemUI/src/com/android/systemui/recents/events/activity/MultiWindowStateChangedEvent.java

@@ -25,10 +25,14 @@ import com.android.systemui.recents.model.TaskStack;
 public class MultiWindowStateChangedEvent extends EventBus.AnimatedEvent {
 
     public final boolean inMultiWindow;
+    // This flag is only used when undocking a task
+    public final boolean showDeferredAnimation;
     public final TaskStack stack;
 
-    public MultiWindowStateChangedEvent(boolean inMultiWindow, TaskStack stack) {
+    public MultiWindowStateChangedEvent(boolean inMultiWindow, boolean showDeferredAnimation,
+            TaskStack stack) {
         this.inMultiWindow = inMultiWindow;
+        this.showDeferredAnimation = showDeferredAnimation;
         this.stack = stack;
     }
 }

packages/SystemUI/src/com/android/systemui/recents/views/TaskStackView.java

@@ -1938,7 +1938,7 @@ public class TaskStackView extends FrameLayout implements TaskStack.TaskStackCal
     }
 
     public final void onBusEvent(final MultiWindowStateChangedEvent event) {
-        if (event.inMultiWindow) {
+        if (event.inMultiWindow || !event.showDeferredAnimation) {
             setTasks(event.stack, true /* allowNotifyStackChanges */);
         } else {
             // Reset the launch state before handling the multiwindow change