Add methods to Collection.

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 1d5626cf0c51f650828a260b65d58d0873375495..3cc72d0a2734c6d6af2272be7b3d224c376fbd02 100644
--- a/tools/dom/templates/html/impl/impl_Element.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Element.darttemplate
@@ -117,10 +117,10 @@ class _ChildrenElementList implements List {
     _element.$dom_replaceChild(value, _childElements[index]);
   }
 
-   void set length(int newLength) {
-     // TODO(jacobr): remove children when length is reduced.
-     throw new UnsupportedError('');
-   }
+  void set length(int newLength) {
+    // TODO(jacobr): remove children when length is reduced.
+    throw new UnsupportedError('');
+  }
 
   Element add(Element value) {
     _element.$dom_appendChild(value);
@@ -150,6 +150,31 @@ class _ChildrenElementList implements List {
     throw new UnimplementedError();
   }
 
+  void remove(Object object) {
+    if (object is Element) {
+      Element element = object;
+      if (identical(element.parentNode, this)) {
+        _element.$dom_removeChild(element);
+      }
+    }
+  }
+
+  void removeAll(Iterable elements) {
+    Collections.removeAll(this, elements);
+  }
+
+  void retainAll(Iterable elements) {
+    Collections.retainAll(this, elements);
+  }
+
+  void removeMatching(bool test(Element element)) {
+    Collections.removeMatching(this, test);
+  }
+
+  void retainMatching(bool test(Element element)) {
+    Collections.retainMatching(this, test);
+  }
+
   void removeRange(int start, int rangeLength) {
     throw new UnimplementedError();
   }
@@ -376,6 +401,26 @@ class _FrozenElementList implements List {
     throw new UnsupportedError('');
   }
 
+  void remove(Object element) {
+    throw new UnsupportedError('');
+  }
+
+  void removeAll(Iterable elements) {
+    throw new UnsupportedError('');
+  }
+
+  void retainAll(Iterable elements) {
+    throw new UnsupportedError('');
+  }
+
+  void removeMatching(bool test(Element element)) {
+    throw new UnsupportedError('');
+  }
+
+  void retainMatching(bool test(Element element)) {
+    throw new UnsupportedError('');
+  }
+
   Element get first => _nodeList.first;
 
   Element get last => _nodeList.last;