Two more files with const RegExp.

sdk/lib/_internal/dartdoc/lib/src/markdown/html_renderer.dart

Index: sdk/lib/_internal/dartdoc/lib/src/markdown/html_renderer.dart
diff --git a/sdk/lib/_internal/dartdoc/lib/src/markdown/html_renderer.dart b/sdk/lib/_internal/dartdoc/lib/src/markdown/html_renderer.dart
index 17941d3c75db6edc690a8a64f989dc5e6d183a3a..d44c5f51e4729bfd6ade794f5f9a0cd746207f81 100644
--- a/sdk/lib/_internal/dartdoc/lib/src/markdown/html_renderer.dart
+++ b/sdk/lib/_internal/dartdoc/lib/src/markdown/html_renderer.dart
@@ -8,7 +8,7 @@ String renderToHtml(List<Node> nodes) => new HtmlRenderer().render(nodes);
 
 /// Translates a parsed AST to HTML.
 class HtmlRenderer implements NodeVisitor {
-  static const _BLOCK_TAGS = new RegExp(
+  static final _BLOCK_TAGS = new RegExp(
       'blockquote|h1|h2|h3|h4|h5|h6|hr|p|pre');
 
   StringBuffer buffer;