Incremental compilation: set up inheritance.

dart/pkg/dart2js_incremental/lib/library_updater.dart

Index: dart/pkg/dart2js_incremental/lib/library_updater.dart
diff --git a/dart/pkg/dart2js_incremental/lib/library_updater.dart b/dart/pkg/dart2js_incremental/lib/library_updater.dart
index c206760c08d2304859f34229bc464a199048ed80..df7a85a6dd04a75da8259e242ff5e442e044f3da 100644
--- a/dart/pkg/dart2js_incremental/lib/library_updater.dart
+++ b/dart/pkg/dart2js_incremental/lib/library_updater.dart
@@ -417,7 +417,14 @@ class LibraryUpdater extends JsFeatures {
     }
 
     for (ClassElementX cls in newClasses) {
-      // TODO(ahe): Set up superclasses.
+      if (cls.isObject) continue;
+      jsAst.Node classAccess = namer.elementAccess(cls);
+      jsAst.Node superAccess = namer.elementAccess(cls.superclass);
+
+      updates.add(
+          js.statement(
+              r'self.$dart_unsafe_eval.inheritFrom(#, #)',
+              [classAccess, superAccess]));
     }
 
     for (Element element in compiler.enqueuer.codegen.newlyEnqueuedElements) {