Fix runtime strong mode error in ListMixin

pkg/dev_compiler/test/browser/language_tests.js

Index: pkg/dev_compiler/test/browser/language_tests.js
diff --git a/pkg/dev_compiler/test/browser/language_tests.js b/pkg/dev_compiler/test/browser/language_tests.js
index ea909a4b2c2c167d702320a4fd489f28ae1724cd..c5806098e943838261ac20ec886732b5c3acf424 100644
--- a/pkg/dev_compiler/test/browser/language_tests.js
+++ b/pkg/dev_compiler/test/browser/language_tests.js
@@ -399,6 +399,9 @@ define(['dart_sdk', 'async_helper', 'expect', 'unittest', 'is', 'require'],
       'UC16_test': firefox_fail,
     },
 
+    'lib/collection': {
+    },
+
     'lib/convert': {
       'encoding_test': skip_timeout,