[snapshot] full setup delegate should also be able to deserialize.

src/setup-isolate.h

 // Copyright 2017 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.
 
 namespace v8 {
 namespace internal {
 
 class Builtins;
 class Code;
 class Isolate;
 
 namespace interpreter {
 class Interpreter;
 }  // namespace interpreter
 
 // This class is an abstraction layer around initialization of components
 // that are either deserialized from the snapshot or generated from scratch.
 // Currently this includes builtins and interpreter bytecode handlers.
-// There are three implementations to choose from (at link time):
+// There are two implementations to choose from at link time:
 // - setup-isolate-deserialize.cc: always loads things from snapshot.
-// - setup-isolate-full.cc: always generates things.
-// - setup-isolate-for-tests.cc: does the one or the other, controlled by
-//                               the |create_heap_objects| flag.
+// - setup-isolate-full.cc: loads from snapshot or bootstraps from scratch,
+//                          controlled by the |create_heap_objects| flag.
+// For testing, the implementation in setup-isolate-for-tests.cc can be chosen
+// to force the behavior of setup-isolate-full.cc at runtime.
 //
 // The actual implementations of generation of builtins and handlers is in
 // setup-builtins-internal.cc and setup-interpreter-internal.cc, and is
 // linked in by the latter two Delegate implementations.
 class SetupIsolateDelegate {
  public:
   SetupIsolateDelegate() {}
   virtual ~SetupIsolateDelegate() {}
 
   virtual void SetupBuiltins(Isolate* isolate, bool create_heap_objects);
 
   virtual void SetupInterpreter(interpreter::Interpreter* interpreter,
                                 bool create_heap_objects);
 
  protected:
   static void SetupBuiltinsInternal(Isolate* isolate);
   static void AddBuiltin(Builtins* builtins, int index, Code* code);
 };
 
 }  // namespace internal
 }  // namespace v8