ValueSerializer: Expose reading/writing doubles to embedder.

src/value-serializer.cc

Index: src/value-serializer.cc
diff --git a/src/value-serializer.cc b/src/value-serializer.cc
index edbc75795fa17dffe7aaee88d0eb03411d50aab4..1d2e36dc043a442728231a7c57d5fb924bf5ee31 100644
--- a/src/value-serializer.cc
+++ b/src/value-serializer.cc
@@ -903,6 +903,10 @@ bool ValueDeserializer::ReadUint64(uint64_t* value) {
   return ReadVarint<uint64_t>().To(value);
 }
 
+bool ValueDeserializer::ReadDouble(double* value) {
+  return ReadDouble().To(value);
+}
+
 bool ValueDeserializer::ReadRawBytes(size_t length, const void** data) {
   if (length > static_cast<size_t>(end_ - position_)) return false;
   *data = position_;