[proxies] Teach ToPropertyDescriptor to deal with Proxies

src/property-descriptor.h

Index: src/property-descriptor.h
diff --git a/src/property-descriptor.h b/src/property-descriptor.h
index 9425ab10ef0262f65101f314465afc67e819202b..5fbbfa36ec263de2412a0fad6383d59f118c6c64 100644
--- a/src/property-descriptor.h
+++ b/src/property-descriptor.h
@@ -41,6 +41,17 @@ class PropertyDescriptor {
     return !IsAccessorDescriptor(desc) && !IsDataDescriptor(desc);
   }
 
+  // ES6 6.2.4.4
+  Handle<Object> ToObject(Isolate* isolate);
+
+  // ES6 6.2.4.5
+  static bool ToPropertyDescriptor(Isolate* isolate, Handle<Object> obj,
+                                   PropertyDescriptor* desc);
+
+  // ES6 6.2.4.6
+  static void CompletePropertyDescriptor(Isolate* isolate,
+                                         PropertyDescriptor* desc);
+
   bool is_empty() const {
     return !has_enumerable() && !has_configurable() && !has_writable() &&
            !has_value() && !has_get() && !has_set();
@@ -89,11 +100,6 @@ class PropertyDescriptor {
         (has_writable() && !writable() ? READ_ONLY : NONE));
   }
 
-  Handle<Object> ToObject(Isolate* isolate);
-
-  static bool ToPropertyDescriptor(Isolate* isolate, Handle<Object> obj,
-                                   PropertyDescriptor* desc);
-
  private:
   bool enumerable_ : 1;
   bool has_enumerable_ : 1;