Introduce DisallowDeoptimization scope.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index f3946d3b7ad03edaa3626c02ce348687541c951e..50a80467e41cd33f76ca9302548f00d5b82c17f0 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -14583,6 +14583,7 @@ RUNTIME_FUNCTION(Runtime_TryMigrateInstance) {
   // code where we can't handle lazy deopts for lack of a suitable bailout
   // ID. So we just try migration and signal failure if necessary,
   // which will also trigger a deopt.
+  DisallowDeoptimization no_deoptimization(isolate);
   if (!JSObject::TryMigrateInstance(js_object)) return Smi::FromInt(0);

[Yang, 2014/04/28 06:38:38]

Isn't JSObject::TryMigrateInstance not supposed to cause deopts altogether? In
that case, moving the disallow scope inside it would be nicer. If not, ignore
this comment.

[Benedikt Meurer, 2014/04/28 06:44:36]

Done.

   return *object;
 }