WIP: Allow ValueSerializer clients to transfer long strings out of band.

src/value-serializer.h

Index: src/value-serializer.h
diff --git a/src/value-serializer.h b/src/value-serializer.h
index ef424698d0e59d10323d4f5a136ffcabb5710881..393fe2b73bbf190a58c283f93b443427f922c86c 100644
--- a/src/value-serializer.h
+++ b/src/value-serializer.h
@@ -94,6 +94,16 @@ class ValueSerializer {
    */
   void SetTreatArrayBufferViewsAsHostObjects(bool mode);
 
+  /*
+   * If a positive values is assigned, strings of at least that length will be
+   * passed to the delegate instead of serialized inline into the buffer.
+   * This option is recommended only if the delegate has a more efficient means
+   * of delivering those strings. By default, this feature is disabled.
+   */
+  void SetMinimumLongStringLength(int length) {
+    long_string_threshold_ = length;
+  }
+
  private:
   // Managing allocations of the internal buffer.
   Maybe<bool> ExpandBuffer(size_t required_capacity);
@@ -112,7 +122,7 @@ class ValueSerializer {
   void WriteOddball(Oddball* oddball);
   void WriteSmi(Smi* smi);
   void WriteHeapNumber(HeapNumber* number);
-  void WriteString(Handle<String> string);
+  Maybe<bool> WriteString(Handle<String> string);
   Maybe<bool> WriteJSReceiver(Handle<JSReceiver> receiver) WARN_UNUSED_RESULT;
   Maybe<bool> WriteJSObject(Handle<JSObject> object) WARN_UNUSED_RESULT;
   Maybe<bool> WriteJSObjectSlow(Handle<JSObject> object) WARN_UNUSED_RESULT;
@@ -164,6 +174,10 @@ class ValueSerializer {
   // A similar map, for transferred array buffers.
   IdentityMap<uint32_t, ZoneAllocationPolicy> array_buffer_transfer_map_;
 
+  // Used for tracking long strings.
+  int long_string_threshold_ = -1;
+  IdentityMap<uint32_t, ZoneAllocationPolicy> long_string_map_;
+
   DISALLOW_COPY_AND_ASSIGN(ValueSerializer);
 };
 
@@ -212,6 +226,12 @@ class ValueDeserializer {
                            Handle<JSArrayBuffer> array_buffer);
 
   /*
+   * Accepts a long string corresponding to one passed previously to
+   * ValueSerializer::Delegate::GetLongStringId.
+   */
+  void TransferLongString(uint32_t transfer_id, Handle<String> string);
+
+  /*
    * Publicly exposed wire format writing methods.
    * These are intended for use within the delegate's WriteHostObject method.
    */
@@ -254,6 +274,7 @@ class ValueDeserializer {
   MaybeHandle<String> ReadUtf8String() WARN_UNUSED_RESULT;
   MaybeHandle<String> ReadOneByteString() WARN_UNUSED_RESULT;
   MaybeHandle<String> ReadTwoByteString() WARN_UNUSED_RESULT;
+  MaybeHandle<String> ReadLongString() WARN_UNUSED_RESULT;
   MaybeHandle<JSObject> ReadJSObject() WARN_UNUSED_RESULT;
   MaybeHandle<JSArray> ReadSparseJSArray() WARN_UNUSED_RESULT;
   MaybeHandle<JSArray> ReadDenseJSArray() WARN_UNUSED_RESULT;
@@ -296,6 +317,7 @@ class ValueDeserializer {
   // Always global handles.
   Handle<FixedArray> id_map_;
   MaybeHandle<SeededNumberDictionary> array_buffer_transfer_map_;
+  MaybeHandle<SeededNumberDictionary> long_string_map_;
 
   DISALLOW_COPY_AND_ASSIGN(ValueDeserializer);
 };