Follow object map transitions when deserializing object properties.

test/unittests/value-serializer-unittest.cc

Index: test/unittests/value-serializer-unittest.cc
diff --git a/test/unittests/value-serializer-unittest.cc b/test/unittests/value-serializer-unittest.cc
index 9f1aa2fa9999237dcd578e88cf8deb978c141875..41e5ba01435322994cb0266195723a148316c49f 100644
--- a/test/unittests/value-serializer-unittest.cc
+++ b/test/unittests/value-serializer-unittest.cc
@@ -50,6 +50,21 @@ class ValueSerializerTest : public TestWithIsolate {
                   output_functor);
   }
 
+  // Variant which uses JSON.parse/stringify to check the result.
+  void RoundTripJSON(const char* source) {
+    RoundTripTest(
+        [this, source]() {
+          return JSON::Parse(serialization_context_, StringFromUtf8(source))
+              .ToLocalChecked();
+        },
+        [this, source](Local<Value> value) {
+          ASSERT_TRUE(value->IsObject());
+          EXPECT_EQ(source, Utf8Value(JSON::Stringify(deserialization_context_,
+                                                      value.As<Object>())
+                                          .ToLocalChecked()));
+        });
+  }
+
   Maybe<std::vector<uint8_t>> DoEncode(Local<Value> value) {
     Local<Context> context = serialization_context();
     ValueSerializer serializer(isolate());
@@ -656,6 +671,23 @@ TEST_F(ValueSerializerTest, RoundTripTrickyGetters) {
                     });
 }
 
+TEST_F(ValueSerializerTest, RoundTripDictionaryObjectForTransitions) {
+  // A case which should run on the fast path, and should reach all of the
+  // different cases:
+  // - expected transition matched
+  // - expected transition failed to match
+  // - transition found (of multiple possible)
+  // - no known transition

[Camillo Bruni, 2016/09/14 16:26:20]

nit: can you update the order of the comment, so it matches the test?

1. xyz (no known transition as this is the first time we create this kind of
object)
2. xyz (full simple transition matches)
3. xyw (transition partially matches, w is not found, causing fallback)
4. xyz (transition matches, with xy being simple transition, and w a full
transition)
5. xyw (same)

[jbroman, 2016/09/14 19:07:16]

Done.

+  RoundTripJSON(
+      "[{\"x\":1,\"y\":2,\"z\":3},{\"x\":4,\"y\":5,\"z\":6},{\"x\":5,\"y\":6,"
+      "\"w\":7},{\"x\":6,\"y\":7,\"z\":8},{\"x\":0,\"y\":0,\"w\":0}]");

[Camillo Bruni, 2016/09/14 16:26:20]

late question: single quotes doesn't work for the properties here?
nit: could you force newlines whenever a new object starts? This makes reading
this way easier.

There are two more cases I would like to have a test for, just in case :)
nit: can you test the path of adding more properties after a complex transition
succeeded (xywz)
int: can you test the path of adding more properties after a complex transition
wasn't found (zykz)

[jbroman, 2016/09/14 19:07:16]

This uses JSON::Parse/Stringify to compare the object before/after doing a
serialization round trip (because there aren't many easy ways to do a  deep
comparison), so this needs to match the JSON output verbatim, and that means
double quotes.
But I can wrap more nicely than clang-format's default, and I've done that.
Done.

+  // A slightly simpler case that uses two-byte strings.
+  RoundTripJSON(
+      "[{\"\xF0\x9F\x91\x8A\":1,\"\xF0\x9F\x91\x8B\":2},{\"\xF0\x9F\x91\x8A\":"
+      "3,\"\xF0\x9F\x91\x8C\":4},{\"\xF0\x9F\x91\x8A\":5,\"\xF0\x9F\x91\x9B\":"
+      "6}]");
+}
+
 TEST_F(ValueSerializerTest, DecodeDictionaryObjectVersion0) {
   // Empty object.
   DecodeTestForVersion0(