ValueSerializer: add kOneByteString to expected key fast path.

src/value-serializer.cc

Index: src/value-serializer.cc
diff --git a/src/value-serializer.cc b/src/value-serializer.cc
index acedb4be329fcdf570785051993adbe95b7bef46..59e9b1031ec91930c0515e3ae1c3af1f1c319af2 100644
--- a/src/value-serializer.cc
+++ b/src/value-serializer.cc
@@ -1261,10 +1261,9 @@ bool ValueDeserializer::ReadExpectedString(Handle<String> expected) {
 
   // If the bytes are verbatim what is in the flattened string, then the string
   // is successfully consumed.
-  if (tag == SerializationTag::kUtf8String && flat.IsOneByte()) {
+  if (tag == SerializationTag::kOneByteString && flat.IsOneByte()) {
     Vector<const uint8_t> chars = flat.ToOneByteVector();
     if (byte_length == static_cast<size_t>(chars.length()) &&
-        String::IsAscii(chars.begin(), chars.length()) &&
         memcmp(bytes.begin(), chars.begin(), byte_length) == 0) {
       return true;
     }
@@ -1274,6 +1273,13 @@ bool ValueDeserializer::ReadExpectedString(Handle<String> expected) {
         memcmp(bytes.begin(), chars.begin(), byte_length) == 0) {
       return true;
     }
+  } else if (tag == SerializationTag::kUtf8String && flat.IsOneByte()) {
+    Vector<const uint8_t> chars = flat.ToOneByteVector();
+    if (byte_length == static_cast<size_t>(chars.length()) &&
+        String::IsAscii(chars.begin(), chars.length()) &&
+        memcmp(bytes.begin(), chars.begin(), byte_length) == 0) {
+      return true;
+    }
   }
 
   position_ = original_position;