Revert "Fix a few strong mode errors in dart:html"

tools/dom/scripts/systemhtml.py

Index: tools/dom/scripts/systemhtml.py
diff --git a/tools/dom/scripts/systemhtml.py b/tools/dom/scripts/systemhtml.py
index 2e0066a17aabb6f95fbff22d138964fe34c5d9c8..efceff66ac78b2067fdbd8f14cbe5329cbd014fd 100644
--- a/tools/dom/scripts/systemhtml.py
+++ b/tools/dom/scripts/systemhtml.py
@@ -908,15 +908,6 @@ class Dart2JSBackend(HtmlDartGenerator):
       self._AddAttributeUsingProperties(attribute, html_name, read_only)
       return
 
-    # If the attribute is shadowed incompatibly in a subclass then we also
-    # can't just generate it as a field. In particular, this happens with
-    # DomMatrixReadOnly and its subclass DomMatrix. Force the superclass
-    # to generate getters. Hardcoding the known problem classes for now.
-    # TODO(alanknight): Fix this more generally.
-    if (self._interface.id == 'DOMMatrixReadOnly' or self._interface.id == 'DOMPointReadOnly'):
-        self._AddAttributeUsingProperties(attribute, html_name, read_only)
-        return
-
     # If the type has a conversion we need a getter or setter to contain the
     # conversion code.
     if (self._OutputConversion(attribute.type.id, attribute.id) or