ValueSerializer: promote scheduled exception if the caller throws one.

v8::Isolate::Throw only schedules the exception; it is necessary to promote it
after invoking the delegate.

BUG=chromium:148757

Review-Url: https://codereview.chromium.org/2332843003
Cr-Commit-Position: refs/heads/master@{#39395}

src/value-serializer.cc

@@ -744,6 +744,9 @@ void ValueSerializer::ThrowDataCloneError(
     isolate_->Throw(
         *isolate_->factory()->NewError(isolate_->error_function(), message));
   }
+  if (isolate_->has_scheduled_exception()) {
+    isolate_->PromoteScheduledException();
+  }
 }
 
 ValueDeserializer::ValueDeserializer(Isolate* isolate,