ValueSerializer: Expose reading/writing doubles to embedder.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index b752a4340eff51dfd9d08d8f06b4b74cf0a56c43..36edf5334a9d27c4cec2ba8238eab8ee808dea8e 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -1789,6 +1789,7 @@ class V8_EXPORT ValueSerializer {
    */
   void WriteUint32(uint32_t value);
   void WriteUint64(uint64_t value);
+  void WriteDouble(double value);
   void WriteRawBytes(const void* source, size_t length);
 
  private:
@@ -1875,6 +1876,7 @@ class V8_EXPORT ValueDeserializer {
    */
   V8_WARN_UNUSED_RESULT bool ReadUint32(uint32_t* value);
   V8_WARN_UNUSED_RESULT bool ReadUint64(uint64_t* value);
+  V8_WARN_UNUSED_RESULT bool ReadDouble(double* value);
   V8_WARN_UNUSED_RESULT bool ReadRawBytes(size_t length, const void** data);
 
  private: