Strong mode changelog updates for 1.23.0

CHANGELOG.md

 ## 1.24.0
 
 ### Language
 
+#### Strong Mode
+
 ### Core library changes
 
 ### Dart VM
 
-### Strong Mode
-
 ### Tool Changes
 
 ## 1.23.0
 
 ### Language
 * Allow using URI strings in `part of` declarations to refer to the
   importing library.
   A library part now can declare its library either as:
   `part of name.of.library;` or as `part of "uriReferenceOfLibrary.dart";`.
   This allows libraries with no library declarations (and therefore no name)
   to have parts, and it allows tools to easily find the library of a part file.
 
-### Core library changes
+#### Strong Mode
 
-* `dart:core`
-  * Added `Uri.isScheme` function to check the scheme of a URI.
-    Example: `uri.isScheme("http")`. Ignores case when comparing.
-  * Make `UriData.parse` validate its input better.
-    If the data is base-64 encoded, the data is normalized wrt.
-    alphabet and padding, and it contains invalid base-64 data,
-    parsing fails. Also normalizes non-base-64 data.
-* `dart:io`
-  * Added functions `File.lastAccessed`, `File.lastAccessedSync`,
-    `File.setLastModified`, `File.setLastModifiedSync`, `File.setLastAccessed`,
-    and `File.setLastAccessedSync`.
-  * Added `{Stdin,Stdout}.supportsAnsiEscapes`.
+* Breaking change - it is now a strong mode error if a mixin causes a name
+  conflict between two private members (field/getter/setter/method) from a
+  different library. (SDK
+  issue [28809](https://github.com/dart-lang/sdk/issues/28809)).
 
-### Dart VM
+lib1.dart:
 
-* Calls to `print()` and `Stdout.write*()` now correctly print unicode
-  characters to the console on Windows. Calls to `Stdout.add*()` behave as
-  before.
 
-### Strong Mode
+```dart
+class A {
+  int _x;
+}
 
-* Strong mode will prefer the expected type to infer generic types,
-  functions, and methods
-  (SDK issue [27586](https://github.com/dart-lang/sdk/issues/27586)).
+class B {
+  int _x;
+}
+```
+
+lib2.dart:
+
+
+```dart
+import 'lib1.dart';
+
+class C extends A with B {}
+```
+
+```
+    error • The private name _x, defined by B, conflicts with the same name defined by A at tmp/lib2.dart:3:24 • private_collision_in_mixin_application
+```
+
+
+* Breaking change - strong mode will prefer the expected type to infer generic
+  types, functions, and methods (SDK
+  issue [27586](https://github.com/dart-lang/sdk/issues/27586)).
 
   ```dart
   main() {
     List<Object> foo = /*infers: <Object>*/['hello', 'world'];
     var bar = /*infers: <String>*/['hello', 'world'];
   }
   ```
 
 * Strong mode inference error messages are improved
   (SDK issue [29108](https://github.com/dart-lang/sdk/issues/29108)).
@@ skipping 25 matching lines @@
     class D extends C {
       int x = 123;
       get y => super.x;
     }
     main() {
       print(new D().x);
       print(new D().y);
     }
     ```
 
+* Strong mode down cast composite warnings are no longer issued by default.
+  (SDK issue [28588](https://github.com/dart-lang/sdk/issues/28588)).
+
+```dart
+void test() {
+  List untyped = [];
+  List<int> typed = untyped; // No down cast composite warning
+}
+```
+
+To opt back into the warnings, add the following to
+the
+[.analysis_options](https://www.dartlang.org/guides/language/analysis-options)
+file for your project.
+
+```
+analyzer:
+  errors:
+    strong_mode_down_cast_composite: warning
+```
+
+
+### Core library changes
+
+* `dart:core`
+  * Added `Uri.isScheme` function to check the scheme of a URI.
+    Example: `uri.isScheme("http")`. Ignores case when comparing.
+  * Make `UriData.parse` validate its input better.
+    If the data is base-64 encoded, the data is normalized wrt.
+    alphabet and padding, and it contains invalid base-64 data,
+    parsing fails. Also normalizes non-base-64 data.
+* `dart:io`
+  * Added functions `File.lastAccessed`, `File.lastAccessedSync`,
+    `File.setLastModified`, `File.setLastModifiedSync`, `File.setLastAccessed`,
+    and `File.setLastAccessedSync`.
+  * Added `{Stdin,Stdout}.supportsAnsiEscapes`.
+
+### Dart VM
+
+* Calls to `print()` and `Stdout.write*()` now correctly print unicode
+  characters to the console on Windows. Calls to `Stdout.add*()` behave as
+  before.
+
 ### Tool changes
 
 * Analysis
   * `dartanalyzer` now follows the same rules as the analysis server to find
     an analysis options file, stopping when an analysis options file is found:
     * Search up the directory hierarchy looking for an analysis options file.
     * If analyzing a project referencing the [Flutter](https://flutter.io/)
       package, then use the
       [default Flutter analysis options](https://github.com/flutter/flutter/blob/master/packages/flutter/lib/analysis_options_user.yaml)
       found in `package:flutter`.
@@ skipping 1710 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.