Prevent double-dismissing of Dismissables, center card_collection under-text

packages/flutter/example/widgets/card_collection.dart

@@ -77,9 +77,8 @@ class CardCollectionApp extends App {
       )
     );
 
-    Widget backgroundText = new Center(
-        child: new Text("Swipe in either direction", style: backgroundTextStyle)
-    );
+    Widget backgroundText =
+      new Text("Swipe in either direction", style: backgroundTextStyle);
 
     // The background Widget appears behind the Dismissable card when the card
     // moves to the left or right. The Positioned widget ensures that the

packages/flutter/lib/widgets/dismissable.dart

@@ -100,6 +100,9 @@ class Dismissable extends StatefulComponent {
   }
 
   EventDisposition _handlePointerDown(sky.PointerEvent event) {
+    if (_fadePerformance.isAnimating)
+      return EventDisposition.processed;
+
     _dragUnderway = true;
     _dragX = 0.0;
     _fadePerformance.progress = 0.0;
@@ -110,6 +113,9 @@ class Dismissable extends StatefulComponent {
     if (!_isActive)
       return EventDisposition.ignored;
 
+    if (_fadePerformance.isAnimating)
+      return EventDisposition.processed;
+
     double oldDragX = _dragX;
     _dragX += event.dx;
     if (oldDragX.sign != _dragX.sign)
@@ -123,6 +129,9 @@ class Dismissable extends StatefulComponent {
     if (!_isActive)
       return EventDisposition.ignored;
 
+    if (_fadePerformance.isAnimating)
+      return EventDisposition.processed;
+
     _dragUnderway = false;
     if (_fadePerformance.isCompleted)
       _startResizePerformance();