[snapshot] serialize embedder-provided external references.

src/external-reference-table.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/external-reference-table.h"
 
 #include "src/accessors.h"
 #include "src/assembler.h"
 #include "src/counters.h"
 #include "src/deoptimizer.h"
@@ skipping 350 matching lines @@
 
   // Add a small set of deopt entry addresses to encoder without generating the
   // deopt table code, which isn't possible at deserialization time.
   HandleScope scope(isolate);
   for (int entry = 0; entry < kDeoptTableSerializeEntryCount; ++entry) {
     Address address = Deoptimizer::GetDeoptimizationEntry(
         isolate, entry, Deoptimizer::LAZY,
         Deoptimizer::CALCULATE_ENTRY_ADDRESS);
     Add(address, "lazy_deopt");
   }
+
+  // Add external references provided by the embedder (a null-terminated array).
+  intptr_t* api_external_references = isolate->api_external_references();
+  if (api_external_references != nullptr) {
+    while (*api_external_references != 0) {
+      Add(reinterpret_cast<Address>(*api_external_references), "<embedder>");
+      api_external_references++;
+    }
+  }
 }
 
 }  // namespace internal
 }  // namespace v8