dart2js: add special getter to Closure class in new emitter.

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 7036bb73a526943aa7b76c7b6428ec600e21bedc..e5b40e47677c1287e55b28bbbaa5902f51ae73e3 100644
--- a/pkg/compiler/lib/src/js_emitter/program_builder.dart
+++ b/pkg/compiler/lib/src/js_emitter/program_builder.dart
@@ -353,6 +353,15 @@ class ProgramBuilder {
       });
     }
 
+    if (element == backend.closureClass) {
+      // We add a special getter here to allow for tearing off a closure from
+      // itself.
+      String name = namer.getterNameFromAccessorName(
+          namer.getMappedInstanceName(Compiler.CALL_OPERATOR_NAME));
+      js.Fun function = js.js('function() { return this; }');
+      callStubs.add(_buildStubMethod(name, function));
+    }
+
     ClassElement implementation = element.implementation;
 
     // MixinApplications run through the members of their mixin. Here, we are