[serializer] Add API to warm up startup snapshot with an additional script.

src/isolate.cc

 // Copyright 2012 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/isolate.h"
 
 #include <stdlib.h>
 
 #include <fstream>  // NOLINT(readability/streams)
 #include <sstream>
@@ skipping 2210 matching lines @@
 
   deoptimizer_data_ = new DeoptimizerData(memory_allocator_);
 
   const bool create_heap_objects = (des == NULL);
   if (create_heap_objects && !heap_.CreateHeapObjects()) {
     V8::FatalProcessOutOfMemory("heap object creation");
     return false;
   }
 
   if (create_heap_objects) {
-    // Terminate the cache array with the sentinel so we can iterate.
+    // Terminate the partial snapshot cache so we can iterate.
     partial_snapshot_cache_.Add(heap_.undefined_value());
   }
 
   InitializeThreadLocal();
 
   bootstrapper_->Initialize(create_heap_objects);
   builtins_.SetUp(this, create_heap_objects);
 
   if (FLAG_log_internal_timer_events) {
     set_event_logger(Logger::DefaultEventLoggerSentinel);
@@ skipping 733 matching lines @@
   // Then check whether this scope intercepts.
   if ((flag & intercept_mask_)) {
     intercepted_flags_ |= flag;
     return true;
   }
   return false;
 }
 
 }  // namespace internal
 }  // namespace v8