[animations] Handle DualTransitionBuilder name conflict with flutter/flutter (#173)

* Handle DualTransitionBuilder conflict with flutter/flutter

Require animations package to use internal version of DualTransitionBuilder to avoid conflicts with flutter/flutter\'s recently merged copy of DualTransitionBuilder'.

* Update changelog and pubspec.yaml
diff --git a/packages/animations/CHANGELOG.md b/packages/animations/CHANGELOG.md
index 765bb80..3fe05cc 100644
--- a/packages/animations/CHANGELOG.md
+++ b/packages/animations/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 All notable changes to this project will be documented in this file.
 
+## [1.1.1] - June 19, 2020
+
+* Hide implementation of `DualTransitionBuilder` as the widget has been implemented in the Flutter framework.
 
 ## [1.1.0] - June 2, 2020
 
diff --git a/packages/animations/lib/src/dual_transition_builder.dart b/packages/animations/lib/src/dual_transition_builder.dart
index 5534a6d..763696b 100644
--- a/packages/animations/lib/src/dual_transition_builder.dart
+++ b/packages/animations/lib/src/dual_transition_builder.dart
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// TODO(shihaohong): Remove DualTransitionBuilder once flutter/flutter's `stable`
+// branch contains DualTransitionBuilder.
+
 import 'package:flutter/widgets.dart';
 
 /// Builder callback used by [DualTransitionBuilder].
diff --git a/packages/animations/lib/src/fade_scale_transition.dart b/packages/animations/lib/src/fade_scale_transition.dart
index b01fa1e..63d217c 100644
--- a/packages/animations/lib/src/fade_scale_transition.dart
+++ b/packages/animations/lib/src/fade_scale_transition.dart
@@ -4,7 +4,9 @@
 
 import 'package:flutter/material.dart';
 
-import 'dual_transition_builder.dart';
+// TODO(shihaohong): Remove DualTransitionBuilder once flutter/flutter's `stable`
+// branch contains DualTransitionBuilder.
+import 'dual_transition_builder.dart' as dual_transition_builder;
 import 'modal.dart';
 import 'utils/curves.dart';
 
@@ -151,7 +153,7 @@
 
   @override
   Widget build(BuildContext context) {
-    return DualTransitionBuilder(
+    return dual_transition_builder.DualTransitionBuilder(
       animation: animation,
       forwardBuilder: (
         BuildContext context,
diff --git a/packages/animations/lib/src/fade_through_transition.dart b/packages/animations/lib/src/fade_through_transition.dart
index f6978e4..aa69f53 100644
--- a/packages/animations/lib/src/fade_through_transition.dart
+++ b/packages/animations/lib/src/fade_through_transition.dart
@@ -4,7 +4,9 @@
 
 import 'package:flutter/material.dart';
 
-import 'dual_transition_builder.dart';
+// TODO(shihaohong): Remove DualTransitionBuilder once flutter/flutter's `stable`
+// branch contains DualTransitionBuilder.
+import 'dual_transition_builder.dart' as dual_transition_builder;
 
 /// Used by [PageTransitionsTheme] to define a page route transition animation
 /// in which the outgoing page fades out, then the incoming page fades in and
@@ -223,7 +225,7 @@
 
   @override
   Widget build(BuildContext context) {
-    return DualTransitionBuilder(
+    return dual_transition_builder.DualTransitionBuilder(
       animation: animation,
       forwardBuilder: (
         BuildContext context,
diff --git a/packages/animations/lib/src/shared_axis_transition.dart b/packages/animations/lib/src/shared_axis_transition.dart
index 3439bd4..7940430 100644
--- a/packages/animations/lib/src/shared_axis_transition.dart
+++ b/packages/animations/lib/src/shared_axis_transition.dart
@@ -7,7 +7,9 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 
-import 'dual_transition_builder.dart';
+// TODO(shihaohong): Remove DualTransitionBuilder once flutter/flutter's `stable`
+// branch contains DualTransitionBuilder.
+import 'dual_transition_builder.dart' as dual_transition_builder;
 import 'utils/curves.dart';
 
 /// Determines which type of shared axis transition is used.
@@ -238,7 +240,7 @@
   @override
   Widget build(BuildContext context) {
     final Color color = fillColor ?? Theme.of(context).canvasColor;
-    return DualTransitionBuilder(
+    return dual_transition_builder.DualTransitionBuilder(
       animation: animation,
       forwardBuilder: (
         BuildContext context,
@@ -264,7 +266,7 @@
           child: child,
         );
       },
-      child: DualTransitionBuilder(
+      child: dual_transition_builder.DualTransitionBuilder(
         animation: ReverseAnimation(secondaryAnimation),
         forwardBuilder: (
           BuildContext context,
diff --git a/packages/animations/pubspec.yaml b/packages/animations/pubspec.yaml
index 5094e34..3635d0f 100644
--- a/packages/animations/pubspec.yaml
+++ b/packages/animations/pubspec.yaml
@@ -1,6 +1,6 @@
 name: animations
 description: Fancy pre-built animations that can easily be integrated into any Flutter application.
-version: 1.1.0
+version: 1.1.1
 homepage: https://github.com/flutter/packages/tree/master/packages/animations
 
 environment:
diff --git a/packages/animations/test/dual_transition_builder_test.dart b/packages/animations/test/dual_transition_builder_test.dart
index 4a1d65e..917ab76 100644
--- a/packages/animations/test/dual_transition_builder_test.dart
+++ b/packages/animations/test/dual_transition_builder_test.dart
@@ -2,7 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:animations/src/dual_transition_builder.dart';
+// TODO(shihaohong): Remove DualTransitionBuilder once flutter/flutter's `stable`
+// branch contains DualTransitionBuilder.
+import 'package:animations/src/dual_transition_builder.dart'
+    as dual_transition_builder;
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
@@ -15,7 +18,7 @@
     );
 
     await tester.pumpWidget(Center(
-      child: DualTransitionBuilder(
+      child: dual_transition_builder.DualTransitionBuilder(
         animation: controller,
         forwardBuilder: (
           BuildContext context,
@@ -85,7 +88,7 @@
     await tester.pumpWidget(Directionality(
       textDirection: TextDirection.ltr,
       child: Center(
-        child: DualTransitionBuilder(
+        child: dual_transition_builder.DualTransitionBuilder(
           animation: controller,
           forwardBuilder: (
             BuildContext context,
@@ -147,7 +150,7 @@
       duration: const Duration(milliseconds: 300),
     );
     await tester.pumpWidget(Center(
-      child: DualTransitionBuilder(
+      child: dual_transition_builder.DualTransitionBuilder(
         animation: controller,
         forwardBuilder: (
           BuildContext context,
@@ -213,7 +216,7 @@
       duration: const Duration(milliseconds: 300),
     );
     await tester.pumpWidget(Center(
-      child: DualTransitionBuilder(
+      child: dual_transition_builder.DualTransitionBuilder(
         animation: controller,
         forwardBuilder: (
           BuildContext context,