Update gallery, fix Cupertino fonts by using GoogleSans instead (#155)

* Update gallery, fix Cupertino fonts

Cupertino fonts fixed by using GoogleSans instead

* remove BUILD.gn

* remove ios and android dirs from web/gallery

* remove meta/flutter_gallery.cmx

* revert provider_shopper/pubspec.lock

* remove gallery's test and tool directories

* update web/gallery README

web/gallery/lib/demo/shrine/backdrop.dart

@@ -22,6 +22,65 @@ const Cubic _kDecelerateCurve = Cubic(0.23, 0.94, 0.41, 1.0);
 const double _kPeakVelocityTime = 0.248210;
 const double _kPeakVelocityProgress = 0.379146;
 
+class _TappableWhileStatusIs extends StatefulWidget {
+  const _TappableWhileStatusIs(
+      this.status, {
+        Key key,
+        this.controller,
+        this.child,
+      }) : super(key: key);
+
+  final AnimationController controller;
+  final AnimationStatus status;
+  final Widget child;
+
+  @override
+  _TappableWhileStatusIsState createState() => _TappableWhileStatusIsState();
+}
+
+class _TappableWhileStatusIsState extends State<_TappableWhileStatusIs> {
+  bool _active;
+
+  @override
+  void initState() {
+    super.initState();
+    widget.controller.addStatusListener(_handleStatusChange);
+    _active = widget.controller.status == widget.status;
+  }
+
+  @override
+  void dispose() {
+    widget.controller.removeStatusListener(_handleStatusChange);
+    super.dispose();
+  }
+
+  void _handleStatusChange(AnimationStatus status) {
+    final bool value = widget.controller.status == widget.status;
+    if (_active != value) {
+      setState(() {
+        _active = value;
+      });
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    Widget child = AbsorbPointer(
+      absorbing: !_active,
+      child: widget.child,
+    );
+
+    if (!_active) {
+      child = FocusScope(
+        canRequestFocus: false,
+        debugLabel: '$_TappableWhileStatusIs',
+        child: child,
+      );
+    }
+    return child;
+  }
+}
+
 class _FrontLayer extends StatelessWidget {
   const _FrontLayer({
     Key key,
@@ -275,12 +334,20 @@ class _BackdropState extends State<Backdrop> with SingleTickerProviderStateMixin
     return Stack(
       key: _backdropKey,
       children: <Widget>[
-        widget.backLayer,
+        _TappableWhileStatusIs(
+          AnimationStatus.dismissed,
+          controller: _controller,
+          child: widget.backLayer,
+        ),
         PositionedTransition(
           rect: _layerAnimation,
           child: _FrontLayer(
             onTap: _toggleBackdropLayerVisibility,
-            child: widget.frontLayer,
+            child: _TappableWhileStatusIs(
+              AnimationStatus.completed,
+              controller: _controller,
+              child: widget.frontLayer,
+            ),
           ),
         ),
       ],