Very simple version of Isolates.

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index d8ab9a53852f0d8d4789fda623e5a59226beacad..0b740c4ea1645c289944b4b0894a3de4ea9d8d14 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -510,6 +510,7 @@ static bool RunIsolate(uword parameter) {
 
     Object& result = Object::Handle();
     result = state->ResolveFunction();
+    bool is_function_spawn = state->library_url() != NULL;
     delete state;
     state = NULL;
     if (result.IsError()) {
@@ -519,7 +520,19 @@ static bool RunIsolate(uword parameter) {
     ASSERT(result.IsFunction());
     Function& func = Function::Handle(isolate);
     func ^= result.raw();
-    result = DartEntry::InvokeFunction(func, Object::empty_array());
+    func = func.ImplicitClosureFunction();
+
+    const Array& args = Array::Handle(Array::New(2));
+    args.SetAt(0, Instance::Handle(func.ImplicitStaticClosure()));
+    args.SetAt(1, is_function_spawn ? Bool::True() : Bool::False());
+
+    const Library& lib = Library::Handle(Library::IsolateLibrary());
+    const String& entry_name = String::Handle(String::New("_startIsolate"));
+    const Function& entry_point =
+        Function::Handle(lib.LookupLocalFunction(entry_name));
+    ASSERT(entry_point.IsFunction() && !entry_point.IsNull());
+
+    result = DartEntry::InvokeFunction(entry_point, args);
     if (result.IsError()) {
       StoreError(isolate, result);
       return false;
@@ -977,8 +990,7 @@ static char* GetRootScriptUri(Isolate* isolate) {
 }
 
 
-IsolateSpawnState::IsolateSpawnState(const Function& func,
-                                     const Function& callback_func)
+IsolateSpawnState::IsolateSpawnState(const Function& func)
     : isolate_(NULL),
       script_url_(NULL),
       library_url_(NULL),
@@ -993,12 +1005,7 @@ IsolateSpawnState::IsolateSpawnState(const Function& func,
 
   const String& func_name = String::Handle(func.name());
   function_name_ = strdup(func_name.ToCString());
-  if (!callback_func.IsNull()) {
-    const String& callback_name = String::Handle(callback_func.name());
-    exception_callback_name_ = strdup(callback_name.ToCString());
-  } else {
-    exception_callback_name_ = strdup("_unhandledExceptionCallback");
-  }
+  exception_callback_name_ = strdup("_unhandledExceptionCallback");
 }