[Isolates] More handle improvements:

src/handles-inl.h

Index: src/handles-inl.h
diff --git a/src/handles-inl.h b/src/handles-inl.h
index fa7f7b8609cd76c190f6f6baf9bc981c1d4391a4..0088d3a379bef788237c1c6fd74b188e9c3dc97f 100644
--- a/src/handles-inl.h
+++ b/src/handles-inl.h
@@ -43,6 +43,11 @@ Handle<T>::Handle(T* obj) {
   location_ = HandleScope::CreateHandle(obj, Isolate::Current());
 }
 
+template<class T>
+Handle<T>::Handle(HeapObject* obj) {
+  location_ = HandleScope::CreateHandle<T>(obj, obj->GetIsolate());
+}
+
 
 template<class T>
 Handle<T>::Handle(T* obj, Isolate* isolate) {
@@ -59,9 +64,36 @@ inline T* Handle<T>::operator*() const {
 }
 
 
+// Helper class to zero out the number of extensions in the handle
+// scope data after it has been saved.
+// This is only necessary for HandleScope constructor to get the right
+// order of effects.
+class HandleScopeDataTransfer {
+ public:
+  typedef v8::ImplementationUtilities::HandleScopeData Data;
+
+  explicit HandleScopeDataTransfer(Data* data) : data_(data) {}
+  ~HandleScopeDataTransfer() { data_->extensions = 0; }
+
+  // Called before the destructor to get the data to save.
+  Data* data() { return data_; }
+
+ private:
+  Data* data_;
+
+  DISALLOW_COPY_AND_ASSIGN(HandleScopeDataTransfer);
+};
+
+
 HandleScope::HandleScope()
-    : previous_(*Isolate::Current()->handle_scope_data()) {
-  Isolate::Current()->handle_scope_data()->extensions = 0;
+    : previous_(*HandleScopeDataTransfer(
+        Isolate::Current()->handle_scope_data()).data()) {
+}
+
+
+HandleScope::HandleScope(Isolate* isolate)
+    : previous_(*HandleScopeDataTransfer(isolate->handle_scope_data()).data()) {
+  ASSERT(isolate == Isolate::Current());
 }