Make Script non-TraceWrapperBase and add a comment about ModuleScript tracing

third_party/WebKit/Source/core/dom/ModuleScript.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ModuleScript_h
 #define ModuleScript_h
 
 #include "bindings/core/v8/ScriptModule.h"
 #include "bindings/core/v8/ScriptValue.h"
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "bindings/core/v8/TraceWrapperV8Reference.h"
 #include "core/CoreExport.h"
 #include "core/dom/Script.h"
 #include "platform/heap/Handle.h"
 #include "platform/loader/fetch/ResourceLoaderOptions.h"
 #include "platform/weborigin/KURL.h"
 #include "public/platform/WebURLRequest.h"
 
 namespace blink {
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#concept-module-script-instantiation-state
 enum class ModuleInstantiationState {
   kUninstantiated,
   kErrored,
   kInstantiated,
 };
 
 // ModuleScript is a model object for the "module script" spec concept.
 // https://html.spec.whatwg.org/multipage/webappapis.html#module-script
-class CORE_EXPORT ModuleScript final : public Script {
+class CORE_EXPORT ModuleScript final : public Script, public TraceWrapperBase {
  public:
   static ModuleScript* Create(
       ScriptModule record,
       const KURL& base_url,
       const String& nonce,
       ParserDisposition parser_state,
       WebURLRequest::FetchCredentialsMode credentials_mode) {
     return new ModuleScript(record, base_url, nonce, parser_state,
                             credentials_mode);
   }
@@ skipping 10 matching lines @@
   void SetInstantiationSuccess();
   void SetInstantiationError(v8::Isolate*, v8::Local<v8::Value> error);
 
   ParserDisposition ParserState() const { return parser_state_; }
   WebURLRequest::FetchCredentialsMode CredentialsMode() const {
     return credentials_mode_;
   }
   const String& Nonce() const { return nonce_; }
 
   DECLARE_TRACE();
-  DECLARE_VIRTUAL_TRACE_WRAPPERS();
+  DECLARE_TRACE_WRAPPERS();
 
  private:
   ModuleScript(ScriptModule record,
                const KURL& base_url,
                const String& nonce,
                ParserDisposition parser_state,
                WebURLRequest::FetchCredentialsMode credentials_mode)
       : record_(record),
         base_url_(base_url),
         instantiation_error_(this),
@@ skipping 17 matching lines @@
   ScriptModule record_;
 
   // https://html.spec.whatwg.org/multipage/webappapis.html#concept-module-script-base-url
   const KURL base_url_;
 
   // https://html.spec.whatwg.org/multipage/webappapis.html#concept-module-script-instantiation-state
   ModuleInstantiationState instantiation_state_ =
       ModuleInstantiationState::kUninstantiated;
 
   // https://html.spec.whatwg.org/multipage/webappapis.html#concept-module-script-instantiation-error
+  //
+  // |instantiation_error_| is TraceWrappers()ed and kept alive via the path of
+  // v8::Context -> PerContextData -> Modulator/ModulatorImpl
+  // -> ModuleMap -> ModuleMap::Entry -> ModuleScript -> instantiation_error_.
+  // All the classes/references on the path above should be
+  // TraceWrapperBase/TraceWrapperMember<>/etc.,
+  // but other references to those classes can be normal Member<>.
   TraceWrapperV8Reference<v8::Value> instantiation_error_;
 
   // https://html.spec.whatwg.org/multipage/webappapis.html#concept-module-script-nonce
   const String nonce_;
 
   // https://html.spec.whatwg.org/multipage/webappapis.html#concept-module-script-parser
   const ParserDisposition parser_state_;
 
   // https://html.spec.whatwg.org/multipage/webappapis.html#concept-module-script-credentials-mode
   const WebURLRequest::FetchCredentialsMode credentials_mode_;
 };
 
 }  // namespace blink
 
 #endif