Display negate operators correctly in dartdoc.

utils/dartdoc/dartdoc.dart

Index: utils/dartdoc/dartdoc.dart
diff --git a/utils/dartdoc/dartdoc.dart b/utils/dartdoc/dartdoc.dart
index 4e0f7a6f2cddf29311041df15562cc39ddec25f8..42040dcbddd7ba7c6c3a40b5017db7e80c031200 100644
--- a/utils/dartdoc/dartdoc.dart
+++ b/utils/dartdoc/dartdoc.dart
@@ -520,6 +520,9 @@ class Dartdoc {
     } else if (name.startsWith('set:')) {
       // Setter.
       name = 'set ${name.substring(4)}';
+    } else if (name == ':negate') {
+      // Dart uses 'negate' for prefix negate operators, not '!'.
+      name = 'operator negate';
     } else {
       // See if it's an operator.
       name = TokenKind.rawOperatorFromMethod(name);