Ignore mirrors without valid names.

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index 42329d6cc2932d3b7e04f4502b957a0ff5cdee81..8ae17712c11f59d627a603dc087d106b4ddadf48 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -38089,6 +38089,7 @@ class _Utils {
     var libraryMirror = classMirror.owner;
     classMirror.declarations.forEach((symbol, declaration) {
       var name = _getShortSymbolName(symbol, declaration);
+      if (name.isEmpty) return;
       if (declaration is VariableMirror) {
         if (accessorPropertiesOnly) return;
         if (!declaration.isStatic) return;
@@ -38166,6 +38167,7 @@ class _Utils {
     declarations.forEach((Symbol symbol, Mirror declaration) {
       if (declaration is TypedefMirror || declaration is ClassMirror) return;
       var name = _getShortSymbolName(symbol, declaration);
+      if (name.isEmpty) return;
       bool isField = declaration is VariableMirror ||
           (declaration is MethodMirror &&
               treatPropertyAsField(declaration, libraryMirror));