Generator objects can suspend

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index d20eba58fc91117e4bac2bd39898905b1c25cd3c..4bc2009d0a372c3b229ef8b27fe8414eba69cfb7 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6264,10 +6264,14 @@ class JSGeneratorObject: public JSObject {
   // [function]: The function corresponding to this generator object.
   DECL_ACCESSORS(function, JSFunction)
 
-  // [context]: The context of the suspended computation, or undefined.
-  DECL_ACCESSORS(context, Object)
+  // [context]: The context of the suspended computation.
+  DECL_ACCESSORS(context, Context)
 
   // [continuation]: Offset into code of continuation.
+  //
+  // A positive offset indicates a suspended generator.  The special
+  // kGeneratorExecuting and kGeneratorClosed values indicate that a generator
+  // cannot be resumed.
   inline int continuation();
   inline void set_continuation(int continuation);
 
@@ -6281,6 +6285,10 @@ class JSGeneratorObject: public JSObject {
   DECLARE_PRINTER(JSGeneratorObject)
   DECLARE_VERIFIER(JSGeneratorObject)
 
+  // Magic sentinel values for the continuation.
+  static const int kGeneratorExecuting = -1;
+  static const int kGeneratorClosed = 0;
+
   // Layout description.
   static const int kFunctionOffset = JSObject::kHeaderSize;
   static const int kContextOffset = kFunctionOffset + kPointerSize;