add use counters for __defineGetter__ failing

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index d1cbbc4b3ffb638d34dea2bf22f7210d5f8f3f97..7c614af97b19da1afaf3e29c35c9dfa1600c71ee 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -1708,6 +1708,9 @@ Object* ObjectDefineAccessor(Isolate* isolate, Handle<Object> object,
   Maybe<bool> success = JSReceiver::DefineOwnProperty(
       isolate, receiver, name, &desc, Object::DONT_THROW);
   MAYBE_RETURN(success, isolate->heap()->exception());
+  if (!success.FromJust()) {

[Dan Ehrenberg, 2016/06/21 00:04:49]

This will crash if there is an exception. Instead, do

success.IsJust() && !success.fromJust()

You can test this by running on a Proxy whose defineProperty trap throws.

[bakkot, 2016/06/21 00:48:34]

MAYBE_RETURN will have returned if success is Nothing, so the IsJust test is
unnecessary.

+    isolate->CountUsage(v8::Isolate::kDefineGetterOrSetterWouldThrow);
+  }
   // 6. Return undefined.
   return isolate->heap()->undefined_value();
 }