Make getKeys, getValues getters (keys, values).

pkg/dartdoc/lib/src/markdown/html_renderer.dart

Index: pkg/dartdoc/lib/src/markdown/html_renderer.dart
diff --git a/pkg/dartdoc/lib/src/markdown/html_renderer.dart b/pkg/dartdoc/lib/src/markdown/html_renderer.dart
index 38db4d09fb89ab8eba806a15f47dd33ad39869c9..70d4239a4f83169eb887e6d345015dcc7eb940e2 100644
--- a/pkg/dartdoc/lib/src/markdown/html_renderer.dart
+++ b/pkg/dartdoc/lib/src/markdown/html_renderer.dart
@@ -35,9 +35,9 @@ class HtmlRenderer implements NodeVisitor {
     buffer.add('<${element.tag}');
 
     // Sort the keys so that we generate stable output.
-    // TODO(rnystrom): This assumes getKeys() returns a fresh mutable
+    // TODO(rnystrom): This assumes keys returns a fresh mutable
     // collection.
-    final attributeNames = element.attributes.getKeys();
+    final attributeNames = element.attributes.keys;
     attributeNames.sort((a, b) => a.compareTo(b));
     for (final name in attributeNames) {
       buffer.add(' $name="${element.attributes[name]}"');