Generator objects have [[Class]] === "Generator"

src/heap.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 250 matching lines @@
   V(identity_hash_string, "v8::IdentityHash")                            \
   V(closure_string, "(closure)")                                         \
   V(use_strict_string, "use strict")                                     \
   V(dot_string, ".")                                                     \
   V(anonymous_function_string, "(anonymous function)")                   \
   V(compare_ic_string, "==")                                             \
   V(strict_compare_ic_string, "===")                                     \
   V(infinity_string, "Infinity")                                         \
   V(minus_infinity_string, "-Infinity")                                  \
   V(hidden_stack_trace_string, "v8::hidden_stack_trace")                 \
-  V(query_colon_string, "(?:)")
+  V(query_colon_string, "(?:)")                                          \
+  V(Generator_string, "Generator")
 
 // Forward declarations.
 class GCTracer;
 class HeapStats;
 class Isolate;
 class WeakObjectRetainer;
 
 
 typedef String* (*ExternalStringTableUpdaterCallback)(Heap* heap,
                                                       Object** pointer);
@@ skipping 2768 matching lines @@
   AssertNoAllocation no_alloc;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_