First version of the new generators implementation.

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index 760bb8e786b38e4c88809900efded5238c72d60f..9ca0f0f306a0eb394fa7cb8e8346cca6bc61cc65 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -2329,7 +2329,8 @@ void Generate_GeneratorPrototypeResume(
   Node* receiver = assembler->Parameter(0);
   Node* value = assembler->Parameter(1);
   Node* context = assembler->Parameter(4);
-  Node* zero = assembler->SmiConstant(Smi::FromInt(0));
+  Node* closed = assembler->SmiConstant(
+      Smi::FromInt(JSGeneratorObject::kGeneratorClosed));
 
   // Check if the {receiver} is actually a JSGeneratorObject.
   Label if_receiverisincompatible(assembler, Label::kDeferred);
@@ -2345,9 +2346,11 @@ void Generate_GeneratorPrototypeResume(
       receiver, JSGeneratorObject::kContinuationOffset);
   Label if_receiverisclosed(assembler, Label::kDeferred),
       if_receiverisrunning(assembler, Label::kDeferred);
-  assembler->GotoIf(assembler->SmiEqual(receiver_continuation, zero),
+  assembler->GotoIf(assembler->SmiEqual(receiver_continuation, closed),
                     &if_receiverisclosed);
-  assembler->GotoIf(assembler->SmiLessThan(receiver_continuation, zero),
+  DCHECK_LT(JSGeneratorObject::kGeneratorExecuting,
+            JSGeneratorObject::kGeneratorClosed);
+  assembler->GotoIf(assembler->SmiLessThan(receiver_continuation, closed),
                     &if_receiverisrunning);
 
   // Resume the {receiver} using our trampoline.