Remove Collection, Collections and clean up List/Set/Queue implementations of retain/remove.

sdk/lib/_internal/compiler/implementation/mirrors/util.dart

Index: sdk/lib/_internal/compiler/implementation/mirrors/util.dart
diff --git a/sdk/lib/_internal/compiler/implementation/mirrors/util.dart b/sdk/lib/_internal/compiler/implementation/mirrors/util.dart
index 34702115571e4fe9208396da173866919e5a0653..7760da1e633cfb90074da26e862d0937c339ff3a 100644
--- a/sdk/lib/_internal/compiler/implementation/mirrors/util.dart
+++ b/sdk/lib/_internal/compiler/implementation/mirrors/util.dart
@@ -45,13 +45,13 @@ abstract class AbstractMap<K,V> implements Map<K,V> {
     return found;
   }
 
-  Collection<K> get keys {
+  Iterable<K> get keys {
     var keys = <K>[];
     forEach((k,_) => keys.add(k));
     return keys;
   }
 
-  Collection<V> get values {
+  Iterable<V> get values {
     var values = <V>[];
     forEach((_,v) => values.add(v));
     return values;