Add a missing dependency on collection.

CHANGELOG.md

+## 0.12.3+7
+
+* Add a missing dependency on the `collection` package.
+
 ## 0.12.3+6
 
+**This version was unpublished due to [issue 287][].**
+
 * Properly report load errors caused by failing to start browsers.
 
 * Substantially increase browser timeouts. These timeouts are the cause of a lot
   of flakiness, and now that they don't block test running there's less harm in
   making them longer.
 
 ## 0.12.3+5
 
+**This version was unpublished due to [issue 287][].**
+
 * Fix a crash when skipping tests because their platforms don't match.
 
 ## 0.12.3+4
 
+**This version was unpublished due to [issue 287][].**
+
 * The compact reporter will update the timer every second, rather than only
   updating it occasionally.
 
 * The compact reporter will now print the full, untruncated test name before any
   errors or prints emitted by a test.
 
 * The expanded reporter will now *always* print the full, untruncated test name.
 
 ## 0.12.3+3
 
+**This version was unpublished due to [issue 287][].**
+
 * Limit the number of test suites loaded at once. This helps ensure that the
   test runner won't run out of memory when running many test suites that each
   load a large amount of code.
 
 ## 0.12.3+2
 
+**This version was unpublished due to [issue 287][].**
+
+[issue 287]: https://github.com/dart-lang/test/issues/287
+
 * Improve the display of syntax errors in VM tests.
 
 * Work around a [Firefox bug][]. Computed styles now work in tests on Firefox.
 
 [Firefox bug]: https://bugzilla.mozilla.org/show_bug.cgi?id=548397
 
 * Fix a bug where VM tests would be loaded from the wrong URLs on Windows (or in
   special circumstances on other operating systems).
 
 ## 0.12.3+1
@@ skipping 179 matching lines @@
 * **NEW!** `expectAsyncUntil` replaces the now deprecated `expectAsyncUntil0`,
     `expectAsyncUntil1` and `expectAsyncUntil2`
 * `TestCase`:
     * Removed properties: `setUp`, `tearDown`, `testFunction`
     * `enabled` is now get-only
     * Removed methods: `pass`, `fail`, `error`
 * `interactive_html_config.dart` has been removed.
 * `runTests`, `tearDown`, `setUp`, `test`, `group`, `solo_test`, and
   `solo_group` now throw a `StateError` if called while tests are running.
 * `rerunTests` has been removed.