- Get rid of RawClosure class and use RawInstance for closures.

vm/dart_api_impl.cc

Index: vm/dart_api_impl.cc
===================================================================
--- vm/dart_api_impl.cc	(revision 13564)
+++ vm/dart_api_impl.cc	(working copy)
@@ -2384,21 +2384,22 @@
   // different signature classes for closures.
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
-  const Object& obj = Object::Handle(isolate, Api::UnwrapHandle(object));
-  return obj.IsClosure();
+  const Instance& closure_obj = Api::UnwrapInstanceHandle(isolate, object);
+  return (!closure_obj.IsNull() && closure_obj.IsClosure());
 }
 
 
 DART_EXPORT Dart_Handle Dart_ClosureFunction(Dart_Handle closure) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
-  const Closure& closure_obj = Api::UnwrapClosureHandle(isolate, closure);
-  if (closure_obj.IsNull()) {
-    RETURN_TYPE_ERROR(isolate, closure, Closure);
+  const Instance& closure_obj = Api::UnwrapInstanceHandle(isolate, closure);
+  if (closure_obj.IsNull() || !closure_obj.IsClosure()) {
+    RETURN_TYPE_ERROR(isolate, closure, Instance);
   }
+
   ASSERT(ClassFinalizer::AllClassesFinalized());
 
-  RawFunction* rf = closure_obj.function();
+  RawFunction* rf = Closure::function(closure_obj);
   return Api::NewHandle(isolate, rf);
 }
 
@@ -2408,9 +2409,9 @@
                                            Dart_Handle* arguments) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
-  const Closure& closure_obj = Api::UnwrapClosureHandle(isolate, closure);
-  if (closure_obj.IsNull()) {
-    RETURN_TYPE_ERROR(isolate, closure, Closure);
+  const Instance& closure_obj = Api::UnwrapInstanceHandle(isolate, closure);
+  if (closure_obj.IsNull() || !closure_obj.IsClosure()) {
+    RETURN_TYPE_ERROR(isolate, closure, Instance);
   }
   if (number_of_arguments < 0) {
     return Api::NewError(