fix missing SDK symbols

pkg/dev_compiler/lib/src/compiler/code_generator.dart

Index: pkg/dev_compiler/lib/src/compiler/code_generator.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/code_generator.dart b/pkg/dev_compiler/lib/src/compiler/code_generator.dart
index e2552798ef4753d54ddc48977344feef0937fdb1..a1b4433119fa4f3449b0f85a17120654ee2bbe4a 100644
--- a/pkg/dev_compiler/lib/src/compiler/code_generator.dart
+++ b/pkg/dev_compiler/lib/src/compiler/code_generator.dart
@@ -1986,11 +1986,10 @@ class CodeGenerator extends Object
   /// Ensure `dartx.` symbols we will use are present.
   void _initExtensionSymbols(ClassElement classElem,
       List<MethodDeclaration> methods, List<FieldDeclaration> fields) {
-    if (_extensionTypes.hasNativeSubtype(classElem.type)) {
+    if (_extensionTypes.hasNativeSubtype(classElem.type) ||
+        classElem.type.isObject) {
       for (var m in methods) {
-        if (!m.isAbstract &&
-            !m.isStatic &&
-            resolutionMap.elementDeclaredByMethodDeclaration(m).isPublic) {
+        if (!m.isAbstract && !m.isStatic && m.element.isPublic) {
           _declareMemberName(m.element, useExtension: true);
         }
       }