Add hold and sweep semantics to gesture arena

packages/flutter/lib/src/gestures/arena.dart

@@ -45,6 +45,7 @@ class GestureArenaEntry {
 class _GestureArenaState {
   final List<GestureArenaMember> members = new List<GestureArenaMember>();
   bool isOpen = true;
+  bool isHeld = false;
 
   void add(GestureArenaMember member) {
     assert(isOpen);
@@ -72,6 +73,32 @@ class GestureArena {
     _tryToResolveArena(key, state);
   }
 
+  /// Force resolution on this arena, giving the win to the first member
+  void sweep(Object key) {
+    _GestureArenaState state = _arenas[key];
+    if (state == null)
+      return;  // This arena either never existed or has been resolved.
+    assert(!state.isOpen);
+    if (state.isHeld)
+      return;  // This arena is being held for a long-lived member
+    if (!state.members.isEmpty) {
+      // First member wins
+      state.members.first.acceptGesture(key);
+      // Give all the other members the bad news
+      for (int i = 1; i < state.members.length; i++)
+        state.members[i].rejectGesture(key);
+    }
+    _arenas.remove(key);
+  }
+
+  /// Prevent the arena from being swept
+  void hold(Object key) {
+    _GestureArenaState state = _arenas[key];
+    if (state == null)
+      return;  // This arena either never existed or has been resolved.
+    state.isHeld = true;
+  }
+
   void _tryToResolveArena(Object key, _GestureArenaState state) {
     assert(_arenas[key] == state);
     assert(!state.isOpen);

packages/flutter/lib/src/rendering/binding.dart

@@ -167,6 +167,8 @@ class FlutterBinding extends HitTestTarget {
       pointerRouter.route(event);
       if (event.type == 'pointerdown')
         GestureArena.instance.close(event.pointer);
+      else if (event.type == 'pointerup')
+        GestureArena.instance.sweep(event.pointer);
     }
   }
 }