ES6 symbols: fix corner cases of equality operators

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 9d6c055c1b33c908c582e1ce193d1e52e2c63803..9fada426d8a63cd04cc0b7688c3f04b9158b7501 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -98,6 +98,10 @@ MaybeObject* Object::ToObject() {
     Isolate* isolate = HeapObject::cast(this)->GetIsolate();
     Context* native_context = isolate->context()->native_context();
     return CreateJSValue(native_context->string_function(), this);
+  } else if (IsSymbol()) {
+    Isolate* isolate = HeapObject::cast(this)->GetIsolate();
+    Context* native_context = isolate->context()->native_context();
+    return CreateJSValue(native_context->symbol_function(), this);
   }
 
   // Throw a type error.