Implement set trap for proxies, and revamp class hierarchy in preparation

src/handles.h

Index: src/handles.h
diff --git a/src/handles.h b/src/handles.h
index 3d930fd74979fa6e8d65e5306c44e3d13565218d..d947b0d6b52039578339b0458354bde370585cbb 100644
--- a/src/handles.h
+++ b/src/handles.h
@@ -185,7 +185,7 @@ void FlattenString(Handle<String> str);
 // string.
 Handle<String> FlattenGetString(Handle<String> str);
 
-Handle<Object> SetProperty(Handle<JSObject> object,
+Handle<Object> SetProperty(Handle<JSReceiver> object,
                            Handle<String> key,
                            Handle<Object> value,
                            PropertyAttributes attributes,
@@ -239,17 +239,13 @@ Handle<Object> SetOwnElement(Handle<JSObject> object,
                              Handle<Object> value,
                              StrictModeFlag strict_mode);
 
-Handle<Object> GetProperty(Handle<JSObject> obj,
+Handle<Object> GetProperty(Handle<JSReceiver> obj,
                            const char* name);
 
 Handle<Object> GetProperty(Handle<Object> obj,
-                           const char* name,
-                           LookupResult* result);
-
-Handle<Object> GetProperty(Handle<Object> obj,
                            Handle<Object> key);
 
-Handle<Object> GetProperty(Handle<JSObject> obj,
+Handle<Object> GetProperty(Handle<JSReceiver> obj,
                            Handle<String> name,
                            LookupResult* result);