Migrate from Input to TextField

We expect TextField to be used much more often than Input. This patch updates
our old example code to use TextField instead.

See #7031

dev/manual_tests/card_collection.dart

@@ -304,9 +304,8 @@ class CardCollectionState extends State<CardCollection> {
           padding: const EdgeInsets.all(kCardMargins),
           child: _editable ?
             new Center(
-              child: new Input(
+              child: new TextField(
                 key: new GlobalObjectKey(cardModel),
-                value: cardModel.inputValue,
                 onChanged: (InputValue value) {
                   setState(() {
                     cardModel.inputValue = value;

examples/flutter_gallery/lib/demo/date_and_time_picker_demo.dart

@@ -117,8 +117,6 @@ class DateAndTimePickerDemo extends StatefulWidget {
 }
 
 class _DateAndTimePickerDemoState extends State<DateAndTimePickerDemo> {
-  InputValue _eventName = InputValue.empty;
-  InputValue _eventLocation = InputValue.empty;
   DateTime _fromDate = new DateTime.now();
   TimeOfDay _fromTime = const TimeOfDay(hour: 7, minute: 28);
   DateTime _toDate = new DateTime.now();
@@ -138,25 +136,13 @@ class _DateAndTimePickerDemoState extends State<DateAndTimePickerDemo> {
             child: new Column(
               crossAxisAlignment: CrossAxisAlignment.stretch,
               children: <Widget>[
-                new Input(
+                new TextField(
                   labelText: 'Event name',
-                  value: _eventName,
                   style: Theme.of(context).textTheme.display1,
-                  onChanged: (InputValue newValue) {
-                    setState(() {
-                      _eventName = newValue;
-                    });
-                  },
                 ),
-                new Input(
+                new TextField(
                   labelText: 'Location',
-                  value: _eventLocation,
                   style: Theme.of(context).textTheme.display1.copyWith(fontSize: 20.0),
-                  onChanged: (InputValue newValue) {
-                    setState(() {
-                      _eventLocation = newValue;
-                    });
-                  },
                 ),
                 new _DateTimePicker(
                   labelText: 'From',

examples/flutter_gallery/lib/demo/text_field_demo.dart

@@ -113,22 +113,12 @@ class TextFieldDemoState extends State<TextFieldDemo> {
         child: new Block(
           padding: const EdgeInsets.symmetric(horizontal: 16.0),
           children: <Widget>[
-            // It's simpler to use an TextField, as below, but a FormField
-            // that builds an Input is equivalent.
-            new FormField<InputValue>(
-              initialValue: InputValue.empty,
+            new TextField(
+              icon: new Icon(Icons.person),
+              hintText: 'What do people call you?',
+              labelText: 'Name',
               onSaved: (InputValue val) { person.name = val.text; },
               validator: _validateName,
-              builder: (FormFieldState<InputValue> field) {
-                return new Input(
-                  icon: new Icon(Icons.person),
-                  hintText: 'What do people call you?',
-                  labelText: 'Name',
-                  value: field.value,
-                  onChanged: field.onChanged,
-                  errorText: field.errorText
-                );
-              },
             ),
             new TextField(
               icon: new Icon(Icons.phone),

examples/stocks/lib/stock_home.dart

@@ -290,8 +290,7 @@ class StockHomeState extends State<StockHome> {
         onPressed: _handleSearchEnd,
         tooltip: 'Back'
       ),
-      title: new Input(
-        value: _searchQuery,
+      title: new TextField(
         autofocus: true,
         hintText: 'Search stocks',
         onChanged: _handleSearchQueryChanged
@@ -336,30 +335,15 @@ class StockHomeState extends State<StockHome> {
   }
 }
 
-class _CreateCompanySheet extends StatefulWidget {
-  @override
-  _CreateCompanySheetState createState() => new _CreateCompanySheetState();
-}
-
-class _CreateCompanySheetState extends State<_CreateCompanySheet> {
-  InputValue _companyName = InputValue.empty;
-
-  void _handleCompanyNameChanged(InputValue value) {
-    setState(() {
-      _companyName = value;
-    });
-  }
-
+class _CreateCompanySheet extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     // TODO(ianh): Fill this out.
     return new Column(
       children: <Widget>[
-        new Input(
+        new TextField(
           autofocus: true,
           hintText: 'Company Name',
-          value: _companyName,
-          onChanged: _handleCompanyNameChanged
         ),
       ]
     );