Don't check for Member.

utils/apidoc/html_diff.dart

Index: utils/apidoc/html_diff.dart
diff --git a/utils/apidoc/html_diff.dart b/utils/apidoc/html_diff.dart
index 93d06bbeb43071375f9ac428aa4d706b0df70a28..8b17f0d35e6215944a3140108e6dfc78c8121273 100644
--- a/utils/apidoc/html_diff.dart
+++ b/utils/apidoc/html_diff.dart
@@ -167,11 +167,9 @@ class HtmlDiff {
       return htmlType.factories[implMember.name];
     } else if ((getter = implMember.name.startsWith('get:')) ||
         (setter = implMember.name.startsWith('set:'))) {
-      // Use getMember to follow interface inheritance chains. If it's a
-      // Member, though, it's an implementation of some data structure
-      // and we don't care about it.
+      // Use getMember to follow interface inheritance chains.
       var htmlProperty = htmlType.getMember(implMember.name.substring(4));
-      if (htmlProperty != null && htmlProperty is! Member) {
+      if (htmlProperty != null) {
         return getter ? htmlProperty.getter : htmlProperty.setter;
       } else {
         return null;