Fix docs.dart, which has been sad and neglected.

tools/dom/docs/bin/docs.dart

Index: tools/dom/docs/bin/docs.dart
diff --git a/tools/dom/docs/bin/docs.dart b/tools/dom/docs/bin/docs.dart
index 697243268ca547d807d3c9141c9838742b445401..6f397832ed90ee9628e91465fbc1b842ea3eb745 100644
--- a/tools/dom/docs/bin/docs.dart
+++ b/tools/dom/docs/bin/docs.dart
@@ -18,10 +18,11 @@ final Path lib_path = scriptDir.append('../../../../sdk/').canonicalize();
 main() {
   print('Converting HTML docs from $lib_path to $json_path.');
 
-  var anyErrors = convert(lib_path, json_path);
-
-  print('Converted HTML docs ${anyErrors ? "with $anyErrors" : "without"}'
-    ' errors.');
+  convert(lib_path, json_path)
+    .then((bool anyErrors) {
+      print('Converted HTML docs ${anyErrors ? "with": "without"}'
+        ' errors.');
+    });
 }
 
 /**
@@ -29,4 +30,4 @@ main() {
  * script.
  */
 Path get scriptDir =>
-    new Path(new Options().script).directoryPath;
+    new Path(new Options().script).directoryPath;