dart2js: Run prepareNativeClasses in the program builder.

pkg/compiler/lib/src/js_emitter/program_builder.dart

Index: pkg/compiler/lib/src/js_emitter/program_builder.dart
diff --git a/pkg/compiler/lib/src/js_emitter/program_builder.dart b/pkg/compiler/lib/src/js_emitter/program_builder.dart
index 4e2f55577e1f5162fdeb4978ad9e506d378751da..81e5e3bec5176c10ea92204c6e2eecf540970e7f 100644
--- a/pkg/compiler/lib/src/js_emitter/program_builder.dart
+++ b/pkg/compiler/lib/src/js_emitter/program_builder.dart
@@ -101,12 +101,23 @@ class ProgramBuilder {
       }
     });
 
+    Map<Class, Map<String, js.Expression>> additionalProperties =
+        new Map<Class, Map<String, js.Expression>>();
+
+    List<Class> neededNativeClasses =
+        _task.nativeEmitter.prepareNativeClasses(
+            nativeClasses,
+            additionalProperties);
+
     _markEagerClasses();
 
-    return new Program(outputs,
-                       nativeClasses,
-                       _task.outputContainsConstantList,
-                       _buildLoadMap());
+    return new Program(
+        outputs,
+        neededNativeClasses,
+        additionalProperties,
+        _buildLoadMap(),
+        outputContainsNativeClasses: neededNativeClasses.isNotEmpty,
+        outputContainsConstantList: _task.outputContainsConstantList);
   }
 
   void _markEagerClasses() {