Mention for-in static checking in CHANGELOG.

CHANGELOG.md

 ## 1.15.0
 
+### Analyzer
+
+*   Static checking of `for in` statements. These will now produce static
+    warnings:
+
+    ```dart
+    // Not Iterable.
+    for (var i in 1234) { ... }
+
+    // String cannot be assigned to int.
+    for (int n in <String>["a", "b"]) { ... }
+
 ### Core library changes
 
 * `dart:async`
   * Made `StreamView` class a `const` class.
 
 * `dart:core`
   * Added `Uri.queryParametersAll` to handle multiple query parameters with
     the same name.
 
 * `dart:io`
@@ skipping 810 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.