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

tools/dom/templates/html/impl/impl_Element.darttemplate

Index: tools/dom/templates/html/impl/impl_Element.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_Element.darttemplate b/tools/dom/templates/html/impl/impl_Element.darttemplate
index f0d30a707aa5aa323a01e9891f3a421d3a386b96..13eaa3080efd68f093803fcdd0f6117fe7b2eb30 100644
--- a/tools/dom/templates/html/impl/impl_Element.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Element.darttemplate
@@ -180,14 +180,6 @@ class _ChildrenElementList extends ListBase<Element> {
     }
   }
 
-  void removeAll(Iterable elements) {
-    _childElements.removeAll(elements);
-  }
-
-  void retainAll(Iterable elements) {
-    _childElements.retainAll(elements);
-  }
-
   void removeWhere(bool test(Element element)) {
     _childElements.removeWhere(test);
   }
@@ -350,14 +342,6 @@ class _FrozenElementList extends ListBase {
     throw new UnsupportedError('');
   }
 
-  void removeAll(Iterable elements) {
-    throw new UnsupportedError('');
-  }
-
-  void retainAll(Iterable elements) {
-    throw new UnsupportedError('');
-  }
-
   void removeWhere(bool test(Element element)) {
     throw new UnsupportedError('');
   }
@@ -515,7 +499,7 @@ $(ANNOTATIONS)abstract class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
    */
   CssClassSet get classes => new _ElementCssClassSet(this);
 
-  void set classes(Collection<String> value) {
+  void set classes(Iterable<String> value) {
     CssClassSet classSet = classes;
     classSet.clear();
     classSet.addAll(value);