Add analysis option that will be used to fix #26583

pkg/analyzer/test/src/task/strong/checker_test.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // TODO(jmesserly): this file needs to be refactored, it's a port from
 // package:dev_compiler's tests
 /// General type checking tests
 library analyzer.test.src.task.strong.checker_test;
 
 import '../../../reflective_tests.dart';
@@ skipping 1882 matching lines @@
   do {} while (/*warning:NON_BOOL_CONDITION*/i);
 
   for (;b;) {}
   for (;/*info:DYNAMIC_CAST*/dyn;) {}
   for (;/*info:DOWN_CAST_IMPLICIT*/obj;) {}
   for (;/*warning:NON_BOOL_CONDITION*/i;) {}
 }
 ''');
   }
 
+  void test_implicitCasts() {
+    addFile('num n; int i = /*info:ASSIGNMENT_CAST*/n;');
+    check();
+    addFile('num n; int i = /*warning:ASSIGNMENT_CAST*/n;');
+    check(implicitCasts: false);
+  }
+
   void test_invalidOverrides_baseClassOverrideToChildInterface() {
     checkFile('''
 class A {}
 class B {}
 
 abstract class I {
     m(A a);
 }
 
 class Base {
@@ skipping 1380 matching lines @@
     // Regression test for https://github.com/dart-lang/sdk/issues/25069
     checkFile('''
 typedef int Foo();
 void foo() {}
 void main () {
   Foo x = /*warning:INVALID_ASSIGNMENT,info:USE_OF_VOID_RESULT*/foo();
 }
 ''');
   }
 }