fix #27408, reverts "ignore dynamic in inference"

CHANGELOG.md

 ## 1.20.0
 
 ### Dart VM
 
 * We have improved the way that the VM locates the native code library for a
   native extension (e.g. `dart-ext:` import). We have updated this
   [article on native extensions](https://www.dartlang.org/articles/dart-vm/native-extensions)
   to reflect the VM's improved behavior.
 
 * Linux builds of the VM will now use the tcmalloc library for memory
@@ skipping 90 matching lines @@
       var b = new Future<B>.value(new B());
       var c = new Future<C>.value(new C());
       var/*infer List<Future<A>>*/ list = [b, c];
       var/*infer List<A>*/ result = await Future.wait(list);
     }
     class A {}
     class B extends A {}
     class C extends A {}
     ```
 
-* Breaking change - ingore `dynamic` when doing inference.
-
-    ```dart
-    main() {
-      dynamic d = 42;
-      List<int> list = /*infer <int>*/[123, /*implicit cast*/d];
-    }
-    ```
-
 ### Tool changes
 
 * `dartfmt` - upgraded to v0.2.10
     * Don't crash on annotations before parameters with trailing commas.
     * Always split enum declarations if they end in a trailing comma.
     * Add `--set-exit-if-changed` to set the exit code on a change.
 
 ## 1.19.0
 
 ### Language changes
@@ skipping 1192 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.