Add support for configuration presets.

CHANGELOG.md

Index: CHANGELOG.md
diff --git a/CHANGELOG.md b/CHANGELOG.md
index f4f6e1285cb1a49fc87a532aac3b2db8dc2740f1..36b1fe594e593e98647b0b2a2cdc916153328963 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 ## 0.12.12
 
+* Add support for [test presets][]. These are defined using the `presets` field
+  in the package configuration file. They can be selected by passing `--preset`
+  or `-P`, or by using the `add_presets` field in the package configuration
+  file.
+
 * Add an `on_os` field to the package configuration file that allows users to
   select different configuration for different operating systems.
 
@@ -10,6 +15,8 @@
   the `test` executable itself is running on iOS, not when it's running browser
   tests on an iOS browser.
 
+[test presets]: https://github.com/dart-lang/test/blob/master/doc/package_config.md#configuration-presets
+
 ## 0.12.11+2
 
 * Update to `shelf_web_socket` 0.2.0.