Remove canTransitionFrom override from Material/CupertinoPageRoute (#45750)

packages/flutter/lib/src/cupertino/route.dart

@@ -176,11 +176,6 @@ class CupertinoPageRoute<T> extends PageRoute<T> {
   @override
   String get barrierLabel => null;
 
-  @override
-  bool canTransitionFrom(TransitionRoute<dynamic> previousRoute) {
-    return previousRoute is CupertinoPageRoute;
-  }
-
   @override
   bool canTransitionTo(TransitionRoute<dynamic> nextRoute) {
     // Don't perform outgoing animation if the next route is a fullscreen dialog.

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

@@ -66,11 +66,6 @@ class MaterialPageRoute<T> extends PageRoute<T> {
   @override
   String get barrierLabel => null;
 
-  @override
-  bool canTransitionFrom(TransitionRoute<dynamic> previousRoute) {
-    return previousRoute is MaterialPageRoute || previousRoute is CupertinoPageRoute;
-  }
-
   @override
   bool canTransitionTo(TransitionRoute<dynamic> nextRoute) {
     // Don't perform outgoing animation if the next route is a fullscreen dialog.

packages/flutter/test/material/page_test.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/material.dart';
+import 'package:flutter/cupertino.dart' show CupertinoPageRoute;
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -785,4 +786,32 @@ void main() {
     expect(homeTapCount, 2);
     expect(pageTapCount, 1);
   });
+
+  testWidgets('On iOS, a MaterialPageRoute should slide out with CupertinoPageTransition when a compatible PageRoute is pushed on top of it', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/44864.
+
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData(platform: TargetPlatform.iOS),
+        home: Scaffold(
+          appBar: AppBar(title: const Text('Title')),
+        ),
+      ),
+    );
+
+    final Offset titleInitialTopLeft = tester.getTopLeft(find.text('Title'));
+
+    tester.state<NavigatorState>(find.byType(Navigator)).push<void>(
+      CupertinoPageRoute<void>(builder: (BuildContext context) => const Placeholder()),
+    );
+
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 150));
+
+    final Offset titleTransientTopLeft = tester.getTopLeft(find.text('Title'));
+
+    // Title of the first route slides to the left.
+    expect(titleInitialTopLeft.dy, equals(titleTransientTopLeft.dy));
+    expect(titleInitialTopLeft.dx, greaterThan(titleTransientTopLeft.dx));
+  });
 }