Refactor forward transition building

Instead of separate functions for the 0->1 and 1->2 transitions, just
have one function.

packages/flutter/lib/src/material/bottom_sheet.dart

@@ -158,7 +158,7 @@ class _ModalBottomSheetRoute<T> extends PopupRoute<T> {
     return BottomSheet.createPerformance();
   }
 
-  Widget buildPage(BuildContext context) {
+  Widget buildPage(BuildContext context, PerformanceView performance, PerformanceView forwardPerformance) {
     return new _ModalBottomSheet(route: this);
   }
 }

packages/flutter/lib/src/material/dialog.dart

@@ -127,9 +127,11 @@ class _DialogRoute<T> extends PopupRoute<T> {
   bool get barrierDismissable => true;
   Color get barrierColor => Colors.black54;
 
-  Widget buildPage(BuildContext context) => child;
+  Widget buildPage(BuildContext context, PerformanceView performance, PerformanceView forwardPerformance) {
+    return child;
+  }
 
-  Widget buildTransition(BuildContext context, PerformanceView performance, Widget child) {
+  Widget buildTransitions(BuildContext context, PerformanceView performance, PerformanceView forwardPerformance, Widget child) {
     return new FadeTransition(
       performance: performance,
       opacity: new AnimatedValue<double>(0.0, end: 1.0, curve: Curves.easeOut),

packages/flutter/lib/src/material/dropdown.dart

@@ -168,7 +168,9 @@ class _DropDownRoute<T> extends PopupRoute<T> {
   bool get barrierDismissable => true;
   Color get barrierColor => null;
 
-  Widget buildPage(BuildContext context) => new _DropDownMenu(route: this);
+  Widget buildPage(BuildContext context, PerformanceView performance, PerformanceView forwardPerformance) {
+    return new _DropDownMenu(route: this);
+  }
 }
 
 class DropDownMenuItem<T> extends StatelessComponent {

packages/flutter/lib/src/material/page.dart

@@ -53,7 +53,7 @@ class MaterialPageRoute<T> extends PageRoute<T> {
   Color get barrierColor => null;
   bool canTransitionFrom(TransitionRoute nextRoute) => false;
 
-  Widget buildPage(BuildContext context) {
+  Widget buildPage(BuildContext context, PerformanceView performance, PerformanceView forwardPerformance) {
     Widget result = builder(context);
     assert(() {
       if (result == null)
@@ -64,7 +64,7 @@ class MaterialPageRoute<T> extends PageRoute<T> {
     return result;
   }
 
-  Widget buildTransition(BuildContext context, PerformanceView performance, Widget child) {
+  Widget buildTransitions(BuildContext context, PerformanceView performance, PerformanceView forwardPerformance, Widget child) {
     return new _MaterialPageTransition(
       performance: performance,
       child: child

packages/flutter/lib/src/material/popup_menu.dart

@@ -109,7 +109,9 @@ class _PopupMenuRoute<T> extends PopupRoute<T> {
   bool get barrierDismissable => true;
   Color get barrierColor => null;
 
-  Widget buildPage(BuildContext context) => new _PopupMenu(route: this);
+  Widget buildPage(BuildContext context, PerformanceView performance, PerformanceView forwardPerformance) {
+    return new _PopupMenu(route: this);
+  }
 }
 
 Future showMenu({ BuildContext context, ModalPosition position, List<PopupMenuItem> items, int elevation: 8 }) {

packages/flutter/lib/src/widgets/routes.dart

@@ -13,7 +13,6 @@ import 'modal_barrier.dart';
 import 'navigator.dart';
 import 'overlay.dart';
 import 'page_storage.dart';
-import 'status_transitions.dart';
 
 const _kTransparent = const Color(0x00000000);
 
@@ -147,11 +146,12 @@ abstract class TransitionRoute<T> extends OverlayRoute<T> {
   }
 
 
-  final ProxyPerformance forwardPerformance = new ProxyPerformance();
+  PerformanceView get forwardPerformance => _forwardPerformance;
+  final ProxyPerformance _forwardPerformance = new ProxyPerformance();
 
   void didPushNext(Route nextRoute) {
     if (nextRoute is TransitionRoute && canTransitionTo(nextRoute) && nextRoute.canTransitionFrom(this)) {
-      PerformanceView current = forwardPerformance.masterPerformance;
+      PerformanceView current = _forwardPerformance.masterPerformance;
       if (current != null) {
         if (current is TrainHoppingPerformance) {
           TrainHoppingPerformance newPerformance;
@@ -159,19 +159,19 @@ abstract class TransitionRoute<T> extends OverlayRoute<T> {
             current.currentTrain,
             nextRoute.performance,
             onSwitchedTrain: () {
-              assert(forwardPerformance.masterPerformance == newPerformance);
+              assert(_forwardPerformance.masterPerformance == newPerformance);
               assert(newPerformance.currentTrain == nextRoute.performance);
-              forwardPerformance.masterPerformance = newPerformance.currentTrain;
+              _forwardPerformance.masterPerformance = newPerformance.currentTrain;
               newPerformance.dispose();
             }
           );
-          forwardPerformance.masterPerformance = newPerformance;
+          _forwardPerformance.masterPerformance = newPerformance;
           current.dispose();
         } else {
-          forwardPerformance.masterPerformance = new TrainHoppingPerformance(current, nextRoute.performance);
+          _forwardPerformance.masterPerformance = new TrainHoppingPerformance(current, nextRoute.performance);
         }
       } else {
-        forwardPerformance.masterPerformance = nextRoute.performance;
+        _forwardPerformance.masterPerformance = nextRoute.performance;
       }
     }
     super.didPushNext(nextRoute);
@@ -180,21 +180,6 @@ abstract class TransitionRoute<T> extends OverlayRoute<T> {
   bool canTransitionTo(TransitionRoute nextRoute) => true;
   bool canTransitionFrom(TransitionRoute nextRoute) => true;
 
-  Widget wrapTransition(BuildContext context, Widget child) {
-    return buildForwardTransition(
-      context,
-      forwardPerformance,
-      buildTransition(
-        context,
-        performance,
-        child
-      )
-    );
-  }
-
-  Widget buildTransition(BuildContext context, PerformanceView performance, Widget child) => child;
-  Widget buildForwardTransition(BuildContext context, PerformanceView performance, Widget child) => child;
-
   String get debugLabel => '$runtimeType';
   String toString() => '$runtimeType(performance: $_performance)';
 }
@@ -270,44 +255,85 @@ class _ModalScopeStatus extends InheritedWidget {
   }
 }
 
-class _ModalScope extends StatusTransitionComponent {
+class _ModalScope extends StatefulComponent {
   _ModalScope({
     Key key,
     this.subtreeKey,
     this.storageBucket,
-    PerformanceView performance,
+    this.performance,
+    this.forwardPerformance,
     this.current,
     this.route
-  }) : super(key: key, performance: performance);
+  }) : super(key: key);
 
   final GlobalKey subtreeKey;
   final PageStorageBucket storageBucket;
+  final PerformanceView performance;
+  final PerformanceView forwardPerformance;
   final bool current;
   final ModalRoute route;
 
+  _ModalScopeState createState() => new _ModalScopeState();
+}
+
+class _ModalScopeState extends State<_ModalScope> {
+  void initState() {
+    super.initState();
+    config.performance?.addStatusListener(_performanceStatusChanged);
+    config.forwardPerformance?.addStatusListener(_performanceStatusChanged);
+  }
+
+  void didUpdateConfig(_ModalScope oldConfig) {
+    if (config.performance != oldConfig.performance) {
+      oldConfig.performance?.removeStatusListener(_performanceStatusChanged);
+      config.performance?.addStatusListener(_performanceStatusChanged);
+    }
+    if (config.forwardPerformance != oldConfig.forwardPerformance) {
+      oldConfig.forwardPerformance?.removeStatusListener(_performanceStatusChanged);
+      config.forwardPerformance?.addStatusListener(_performanceStatusChanged);
+    }
+  }
+
+  void dispose() {
+    config.performance?.removeStatusListener(_performanceStatusChanged);
+    config.forwardPerformance?.removeStatusListener(_performanceStatusChanged);
+    super.dispose();
+  }
+
+  void _performanceStatusChanged(PerformanceStatus status) {
+    setState(() {
+      // The performances' states are our build state, and they changed already.
+    });
+  }
+
   Widget build(BuildContext context) {
     Widget contents = new PageStorage(
-      key: subtreeKey,
-      bucket: storageBucket,
+      key: config.subtreeKey,
+      bucket: config.storageBucket,
       child: new _ModalScopeStatus(
-        current: current,
-        route: route,
-        child: route.buildPage(context)
+        current: config.current,
+        route: config.route,
+        child: config.route.buildPage(context, config.performance, config.forwardPerformance)
       )
     );
-    if (route.offstage) {
+    if (config.route.offstage) {
       contents = new OffStage(child: contents);
     } else {
       contents = new Focus(
-        key: new GlobalObjectKey(route),
+        key: new GlobalObjectKey(config.route),
         child: new IgnorePointer(
-          ignoring: performance.status == PerformanceStatus.reverse,
-          child: route.wrapTransition(context, contents)
+          ignoring: config.performance?.status == PerformanceStatus.reverse,
+          child: config.route.buildTransitions(
+            context,
+            config.performance,
+            config.forwardPerformance,
+            contents
+          )
         )
       );
     }
     contents = new RepaintBoundary(child: contents);
-    ModalPosition position = route.position;
+    ModalPosition position = config.route.position;
     if (position == null)
       return contents;
     return new Positioned(
@@ -347,8 +373,8 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   // The API for subclasses to override - used by _ModalScope
 
   ModalPosition get position => null;
-  Widget buildPage(BuildContext context);
-  Widget buildTransition(BuildContext context, PerformanceView performance, Widget child) {
+  Widget buildPage(BuildContext context, PerformanceView performance, PerformanceView forwardPerformance);
+  Widget buildTransitions(BuildContext context, PerformanceView performance, PerformanceView forwardPerformance, Widget child) {
     return child;
   }
 
@@ -385,7 +411,7 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
 
   // Internals
 
-  final GlobalKey<StatusTransitionState> _scopeKey = new GlobalKey<StatusTransitionState>();
+  final GlobalKey<_ModalScopeState> _scopeKey = new GlobalKey<_ModalScopeState>();
   final GlobalKey _subtreeKey = new GlobalKey();
   final PageStorageBucket _storageBucket = new PageStorageBucket();
 
@@ -408,9 +434,10 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
       subtreeKey: _subtreeKey,
       storageBucket: _storageBucket,
       performance: performance,
+      forwardPerformance: forwardPerformance,
       current: isCurrent,
       route: this
-      // calls buildTransition()/buildForwardTransition() and buildPage(), defined above
+      // calls buildTransitions() and buildPage(), defined above
     );
   }
 

packages/unit/test/widget/page_forward_transitions_test.dart

@@ -30,7 +30,9 @@ class TestRoute<T> extends PageRoute<T> {
   final Widget child;
   Duration get transitionDuration => kMaterialPageRouteTransitionDuration;
   Color get barrierColor => null;
-  Widget buildPage(BuildContext context) => child;
+  Widget buildPage(BuildContext context, PerformanceView performance, PerformanceView forwardPerformance) {
+    return child;
+  }
 }
 
 void main() {