[generators] Decouple generator resume from fullcodegen.

src/runtime/runtime-debug.cc

Index: src/runtime/runtime-debug.cc
diff --git a/src/runtime/runtime-debug.cc b/src/runtime/runtime-debug.cc
index ad8375a8d48225799dc3a6c23cbbd53c947c2a33..a2144ebe7147bb0c917915092fcddcb5c69dbd3a 100644
--- a/src/runtime/runtime-debug.cc
+++ b/src/runtime/runtime-debug.cc
@@ -1598,18 +1598,9 @@ RUNTIME_FUNCTION(Runtime_GetScript) {
 // built-in function such as Array.forEach to enable stepping into the callback,
 // if we are indeed stepping and the callback is subject to debugging.
 RUNTIME_FUNCTION(Runtime_DebugPrepareStepInIfStepping) {
-  DCHECK(args.length() == 1);
   HandleScope scope(isolate);
-  CONVERT_ARG_HANDLE_CHECKED(Object, object, 0);
-  RUNTIME_ASSERT(object->IsJSFunction() || object->IsJSGeneratorObject());
-  Handle<JSFunction> fun;
-  if (object->IsJSFunction()) {
-    fun = Handle<JSFunction>::cast(object);
-  } else {
-    fun = Handle<JSFunction>(
-        Handle<JSGeneratorObject>::cast(object)->function(), isolate);
-  }
-
+  DCHECK_EQ(1, args.length());
+  CONVERT_ARG_HANDLE_CHECKED(JSFunction, fun, 0);
   isolate->debug()->PrepareStepIn(fun);
   return isolate->heap()->undefined_value();
 }