Add a script for determining which DOM methods correspond to which HTML methods.

utils/dartdoc/dartdoc.dart

Index: utils/dartdoc/dartdoc.dart
diff --git a/utils/dartdoc/dartdoc.dart b/utils/dartdoc/dartdoc.dart
index 6ed5d33e04476e8b3d258bd0a15b3b9e98e1a123..51027c0470fa056e3c081ebdde52eba7a8c4f823 100644
--- a/utils/dartdoc/dartdoc.dart
+++ b/utils/dartdoc/dartdoc.dart
@@ -51,7 +51,7 @@ void main() {
   parseOptions('../../frog', [] /* args */, files);
 
   final elapsed = time(() {
-    _comments = <String, Map<int, String>>{};
+    initializeDartDoc();
 
     initializeWorld(files);
 
@@ -81,6 +81,10 @@ void main() {
         '$_totalMembers members in ${elapsed}msec.');
 }
 
+void initializeDartDoc() {
+  _comments = <String, Map<int, String>>{};
+}
+
 /** Copies the static file at 'static/file' to the output directory. */
 copyStatic(String file) {
   var contents = files.readAll(joinPaths('static', file));