Make ScopedPersistent do type conversion.

native_mate/constructor.h

@@ -7,6 +7,7 @@
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
+#include "native_mate/wrappable.h"
 #include "native_mate/function_template.h"
 
 namespace mate {

native_mate/scoped_persistent.h

@@ -18,8 +18,8 @@ class ScopedPersistent {
   ScopedPersistent() {
   }
 
-  explicit ScopedPersistent(v8::Handle<T> handle) {
-    reset(handle);
+  explicit ScopedPersistent(v8::Handle<v8::Value> handle) {
+    reset(v8::Handle<T>::Cast(handle));
   }
 
   ~ScopedPersistent() {
@@ -93,7 +93,7 @@ class RefCountedPersistent : public ScopedPersistent<T>,
  public:
   RefCountedPersistent() {}
 
-  explicit RefCountedPersistent(v8::Handle<T> handle)
+  explicit RefCountedPersistent(v8::Handle<v8::Value> handle)
     : ScopedPersistent<T>(handle) {
   }