Fixed many small formatting errors

isolate_example/lib/page_one.dart

@@ -1,3 +1,17 @@
+// Copyright 2019-present the Flutter authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
@@ -18,24 +32,20 @@ class _PerformancePageState extends State<PerformancePage> {
           SmoothAnimationWidget(),
           Container(
             alignment: Alignment.bottomCenter,
-            padding:
-                EdgeInsets.only(left: 0.0, top: 150.0, right: 0.0, bottom: 0.0),
+            padding: EdgeInsets.only(top: 150.0),
             child: Column(
               children: <Widget>[
                 FutureBuilder<void>(
                   future: computeFuture,
-                  builder: (context, snapshot) {
+                  builder: (BuildContext context, AsyncSnapshot snapshot) {
                     return RaisedButton(
                       child: const Text('Compute on Main'),
                       elevation: 8.0,
                       onPressed: (snapshot.connectionState ==
-                              ConnectionState.done)
-                          ? () {
-                              setState(
-                                () {
-                                  computeFuture = computeOnMainIsolate()
-                                    ..then(
-                                      (_) {
+                          ConnectionState.done) ? () {
+                              setState( () {
+                                computeFuture = computeOnMainIsolate()
+                                    ..then( (_) {
                                         final snackBar1 = SnackBar(
                                           content: Text('Main Isolate Done!'),
                                         );
@@ -52,18 +62,15 @@ class _PerformancePageState extends State<PerformancePage> {
                 ),
                 FutureBuilder<void>(
                   future: computeFuture,
-                  builder: (context, snapshot) {
+                  builder: (BuildContext context, AsyncSnapshot snapshot) {
                     return RaisedButton(
                       child: const Text('Compute on Secondary'),
                       elevation: 8.0,
                       onPressed: (snapshot.connectionState ==
-                              ConnectionState.done)
-                          ? () {
-                              setState(
-                                () {
+                              ConnectionState.done) ? () {
+                              setState( () {
                                   computeFuture = computeOnSecondaryIsolate()
-                                    ..then(
-                                      (_) {
+                                    ..then( (_) {
                                         final snackBar1 = SnackBar(
                                           content:
                                               Text('Secondary Isolate Done!'),
@@ -123,16 +130,13 @@ class SmoothAnimationWidgetState extends State<SmoothAnimationWidget>
     with TickerProviderStateMixin {
   AnimationController _controller;
   var borderRadius;
-  var transitionTween;
 
   @override
   void initState() {
     super.initState();
 
-    _controller =
-        AnimationController(duration: const Duration(seconds: 1), vsync: this)
-          ..addStatusListener(
-            (status) {
+    _controller = AnimationController(duration: const Duration(seconds: 1), vsync: this)
+          ..addStatusListener( (status) {
               if (status == AnimationStatus.completed) {
                 _controller.reverse();
               } else if (status == AnimationStatus.dismissed) {
@@ -154,12 +158,6 @@ class SmoothAnimationWidgetState extends State<SmoothAnimationWidget>
     _controller.forward();
   }
 
-  @override
-  void dispose() {
-    _controller.dispose();
-    super.dispose();
-  }
-
   @override
   Widget build(BuildContext context) {
     return AnimatedBuilder(
@@ -176,7 +174,7 @@ class SmoothAnimationWidgetState extends State<SmoothAnimationWidget>
             decoration: BoxDecoration(
               gradient: LinearGradient(
                 begin: Alignment.topLeft,
-                colors: [
+                colors: <Color>[
                   Colors.blueAccent,
                   Colors.redAccent
                 ], // whitish to gray
@@ -188,4 +186,10 @@ class SmoothAnimationWidgetState extends State<SmoothAnimationWidget>
       },
     );
   }
+
+  @override
+  void dispose() {
+    _controller.dispose();
+    super.dispose();
+  }
 }