fix #27766, allow implicit casts from dynamic to composite types

CHANGELOG.md

 ## 1.21.0
 
 ### Language
 
 * Don't warn about switch case fallthrough if the case ends in a `rethrow`
   statement.
 * Also don't warn if the entire switch case is wrapped in braces - as long as
   the block ends with a `break`, `continue`, `rethrow`, `return` or `throw`.
 * Allow `=` as well as `:` as separator for named parameter default values.
 
 ### Core library changes
 
 * `dart:core`: `Set.difference` now takes a `Set<Object>` as argument.
 
 * `dart:developer`:
   * The service protocol http server can now be controlled from Dart code.
 
 ## 1.20.1 - 2016-10-13
 
 Patch release, resolves one issue:
 
 * Dartium: Fixes a bug that caused crashes.  No issue filed
 
+### Strong Mode
+
+* It is no longer a warning when casting from dynamic to a composite type
+    (SDK issue [27766](https://github.com/dart-lang/sdk/issues/27766)).
+
+    ```dart
+    main() {
+      dynamic obj = <int>[1, 2, 3];
+      // This is now allowed without a warning.
+      List<int> list = obj;
+    }
+    ```
+
 ## 1.20.0 - 2016-10-11
 
 ### 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 1318 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.