Update changelog for override check fixes

Change-Id: Ic2419c1d8d4dabfc96f96f44900d8bcd9c7bab1d
Reviewed-on: https://dart-review.googlesource.com/c/77741
Commit-Queue: Aske Simon Christensen <askesc@google.com>
Reviewed-by: Leaf Petersen <leafp@google.com>

CHANGELOG.md

@@ -4,6 +4,48 @@
 
 ### Language
 
+*   Fixed a bug (issue [32014](http://dartbug.com/32014)) that caused invalid
+    implementations of the interface of a class to not be reported in some cases.
+    For instance, the following code would not produce a compile-time error:
+
+    ```dart
+    class A {
+      num get thing => 2.0;
+    }
+
+    abstract class B implements A {
+      int get thing;
+    }
+
+    class C extends A with B {} // 'thing' from 'A' is not a valid override of 'thing' from 'B'.
+
+    main() {
+      print(new C().thing.isEven); // Expects an int but gets a double.
+    }
+    ```
+
+*   Fixed a bug (issue [34235](http://dartbug.com/34235)) that caused invalid
+    overrides between a mixin member and an overridden member in the superclass
+    of the mixin application to not be reported. For instance, the following
+    code would not produce a compile-time error:
+
+    ```dart
+    class A {
+      int get thing => 2;
+    }
+
+    class B {
+      num get thing => 2.0;
+    }
+
+    class C extends A with B {} // 'thing' from 'B' is not a valid override of 'thing' from 'A'.
+
+    main() {
+      A a = new C();
+      print(a.thing.isEven); // Expects an int but gets a double.
+    }
+    ```
+
 ### Core library changes
 
 #### `dart:core`