SnapshotCreator: start from existing snapshot if we have one

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/builtins/builtins.h"
 #include "src/counters.h"
@@ skipping 28 matching lines @@
 ExternalReferenceTable::ExternalReferenceTable(Isolate* isolate) {
   // nullptr is preserved through serialization/deserialization.
   Add(nullptr, "nullptr");
   AddReferences(isolate);
   AddBuiltins(isolate);
   AddRuntimeFunctions(isolate);
   AddIsolateAddresses(isolate);
   AddAccessors(isolate);
   AddStubCache(isolate);
   AddDeoptEntries(isolate);
+  // API references must be added last.
   AddApiReferences(isolate);
 }
 
 #ifdef DEBUG
 void ExternalReferenceTable::ResetCount() {
   for (ExternalReferenceEntry& entry : refs_) entry.count = 0;
 }
 
 void ExternalReferenceTable::PrintCount() {
   for (int i = 0; i < refs_.length(); i++) {
@@ skipping 393 matching lines @@
     while (*api_external_references != 0) {
       Address address = reinterpret_cast<Address>(*api_external_references);
       Add(address, ResolveSymbol(address));
       api_external_references++;
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8