ValueSerializer: Add an explicit tag for host objects.

test/unittests/value-serializer-unittest.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/value-serializer.h"
 
 #include <algorithm>
 #include <string>
 
 #include "include/v8.h"
@@ skipping 2352 matching lines @@
 
   SerializerDelegate serializer_delegate_;
   DeserializerDelegate deserializer_delegate_;
   ValueSerializer* serializer_;
   ValueDeserializer* deserializer_;
 
   friend class SerializerDelegate;
   friend class DeserializerDelegate;
 };
 
-// This is a tag that's not used in V8.
-const uint8_t ValueSerializerTestWithHostObject::kExampleHostObjectTag = '+';
+// This is a tag that is used in V8. Using this ensures that we have separate
+// tag namespaces.
+const uint8_t ValueSerializerTestWithHostObject::kExampleHostObjectTag = 'T';
 
 TEST_F(ValueSerializerTestWithHostObject, RoundTripUint32) {
   // The host can serialize data as uint32_t.
   EXPECT_CALL(serializer_delegate_, WriteHostObject(isolate(), _))
       .WillRepeatedly(Invoke([this](Isolate*, Local<Object> object) {
         uint32_t value = 0;
         EXPECT_TRUE(object->GetInternalField(0)
                         ->Uint32Value(serialization_context())
                         .To(&value));
         WriteExampleHostObjectTag();
@@ skipping 152 matching lines @@
       }));
   RoundTripTest(
       "({ a: new ExampleHostObject(), get b() { return this.a; }})",
       [this](Local<Value> value) {
         EXPECT_TRUE(EvaluateScriptForResultBool(
             "result.a instanceof ExampleHostObject"));
         EXPECT_TRUE(EvaluateScriptForResultBool("result.a === result.b"));
       });
 }
 
+TEST_F(ValueSerializerTestWithHostObject, DecodeSimpleHostObject) {
+  EXPECT_CALL(deserializer_delegate_, ReadHostObject(isolate()))
+      .WillRepeatedly(Invoke([this](Isolate*) {
+        EXPECT_TRUE(ReadExampleHostObjectTag());
+        return NewHostObject(deserialization_context(), 0, nullptr);
+      }));
+  DecodeTest(
+      {0xff, 0x0d, 0x5c, kExampleHostObjectTag}, [this](Local<Value> value) {
+        EXPECT_TRUE(EvaluateScriptForResultBool(
+            "Object.getPrototypeOf(result) === ExampleHostObject.prototype"));
+      });
+}
+
 class ValueSerializerTestWithHostArrayBufferView
     : public ValueSerializerTestWithHostObject {
  protected:
   void BeforeEncode(ValueSerializer* serializer) override {
     ValueSerializerTestWithHostObject::BeforeEncode(serializer);
     serializer_->SetTreatArrayBufferViewsAsHostObjects(true);
   }
 };
 
 TEST_F(ValueSerializerTestWithHostArrayBufferView, RoundTripUint8ArrayInput) {
@@ skipping 173 matching lines @@
   InvalidDecodeTest(raw);
 }
 
 TEST_F(ValueSerializerTestWithWasm, DecodeWasmModuleWithInvalidDataLength) {
   InvalidDecodeTest({0xff, 0x09, 0x3f, 0x00, 0x57, 0x79, 0x7f, 0x00});
   InvalidDecodeTest({0xff, 0x09, 0x3f, 0x00, 0x57, 0x79, 0x00, 0x7f});
 }
 
 }  // namespace
 }  // namespace v8