ValueSerializer: Replace use of std::vector with a delegate-allocated buffer.

src/value-serializer.h

Index: src/value-serializer.h
diff --git a/src/value-serializer.h b/src/value-serializer.h
index bb483dd7c874f066a971127beecc3533df4e52e9..86e21cf86cbf1eedfb4a94535fe1b8ce93865c95 100644
--- a/src/value-serializer.h
+++ b/src/value-serializer.h
@@ -59,7 +59,13 @@ class ValueSerializer {
    * Returns the stored data. This serializer should not be used once the buffer
    * is released. The contents are undefined if a previous write has failed.
    */
-  std::vector<uint8_t> ReleaseBuffer() { return std::move(buffer_); }
+  std::vector<uint8_t> ReleaseBuffer();
+
+  /*
+   * Returns the buffer, allocated via the delegate, and its size.
+   * Caller assumes ownership of the buffer.
+   */
+  std::pair<uint8_t*, size_t> Release();
 
   /*
    * Marks an ArrayBuffer as havings its contents transferred out of band.
@@ -79,6 +85,9 @@ class ValueSerializer {
   void WriteDouble(double value);
 
  private:
+  // Managing allocations of the internal buffer.
+  void ExpandBuffer(size_t required_capacity);
+
   // Writing the wire format.
   void WriteTag(SerializationTag tag);
   template <typename T>
@@ -126,7 +135,9 @@ class ValueSerializer {
 
   Isolate* const isolate_;
   v8::ValueSerializer::Delegate* const delegate_;
-  std::vector<uint8_t> buffer_;
+  uint8_t* buffer_ = nullptr;
+  size_t buffer_size_ = 0;
+  size_t buffer_capacity_ = 0;
   Zone zone_;
 
   // To avoid extra lookups in the identity map, ID+1 is actually stored in the