Remove unneeded types (#949)

web/charts/lib/axes/line_disjoint_axis.dart

@@ -153,7 +153,7 @@ class DisjointMeasureAxisLineChart extends StatelessWidget {
         primaryMeasureAxis: const charts.NumericAxisSpec(
             tickProviderSpec: charts.StaticNumericTickProviderSpec(
           // Create the ticks to be used the domain axis.
-          <charts.TickSpec<num>>[
+          [
             charts.TickSpec(0, label: ''),
             charts.TickSpec(1, label: ''),
             charts.TickSpec(2, label: ''),

web/charts/lib/axes/statically_provided_ticks.dart

@@ -81,7 +81,7 @@ class StaticallyProvidedTicks extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     // Create the ticks to be used the domain axis.
-    final staticTicks = <charts.TickSpec<String>>[
+    final staticTicks = [
       const charts.TickSpec(
           // Value must match the domain value.
           '2014',

web/charts/lib/drawer.dart

@@ -29,7 +29,7 @@ class GalleryDrawer extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Drawer(
-      child: ListView(children: <Widget>[
+      child: ListView(children: [
         // Performance overlay toggle.
         ListTile(
           leading: const Icon(Icons.assessment),

web/charts/lib/gallery_scaffold.dart

@@ -57,7 +57,7 @@ class _GalleryScaffoldState extends State<GalleryScaffold> {
       appBar: AppBar(title: Text(widget.title)),
       body: Padding(
           padding: const EdgeInsets.all(8.0),
-          child: Column(children: <Widget>[
+          child: Column(children: [
             SizedBox(height: 250.0, child: widget.childBuilder()),
           ])),
       floatingActionButton: FloatingActionButton(