fix #26120, sideways casts no longer supported

CHANGELOG.md

 ## 1.19.0
 
 ### Language changes
 
 * The language now allows a trailing comma after the last argument of a call and
  the last parameter of a function declaration. This can make long argument or
  parameter lists easier to maintain, as commas can be left as-is when
  reordering lines. For details, see SDK issue
  [26644](https://github.com/dart-lang/sdk/issues/26644).
 
@@ skipping 68 matching lines @@
 * Breaking change - smarter inference for async functions
     (SDK issue [25322](https://github.com/dart-lang/sdk/issues/25322)).
 
     ```dart
     void test() async {
       List<int> x = await [4]; // was previously inferred
       List<int> y = await new Future.value([4]); // now inferred too
     }
     ```
 
+* Breaking change - sideways casts are no longer allowed
+    (SDK issue [26120](https://github.com/dart-lang/sdk/issues/26120)).
+
 ### Dart VM
 
 *   The dependency on BoringSSL has been rolled forward. Going forward, builds
     of the Dart VM including secure sockets will require a compiler with C++11
     support, and to link against glibc 2.16 or newer. For details, see the
     [Building wiki page](https://github.com/dart-lang/sdk/wiki/Building).
 
 ### Tool Changes
 
 * `dartfmt` - upgraded to v0.2.9
@@ skipping 1087 matching lines @@
     they will keep the Dart process alive until they time out. This fixes the
     handling of persistent connections. Previously, the client would shut down
     immediately after a request.
 
   * **Breaking change:** `HttpServer` no longer compresses all traffic by
     default. The new `autoCompress` property can be set to `true` to re-enable
     compression.
 
 * `dart:isolate`: `Isolate.spawnUri` added the optional `packageRoot` argument,
   which controls how it resolves `package:` URIs.