[ES6 modules] Introduce ModuleTreeLinker

third_party/WebKit/Source/core/dom/Modulator.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 Modulator_h
 #define Modulator_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "bindings/core/v8/V8PerContextData.h"
 #include "core/CoreExport.h"
@@ skipping 71 matching lines @@
 
   // Asynchronously retrieve a module script from the module map, or fetch it
   // and put it in the map if it's not there already.
   // https://html.spec.whatwg.org/#fetch-a-single-module-script
   virtual void FetchSingle(const ModuleScriptFetchRequest&,
                            ModuleGraphLevel,
                            SingleModuleClient*) = 0;
 
   // Synchronously retrieves a single module script from existing module map
   // entry.
+  // Note: returns nullptr if the module map entry is still "fetching".
   virtual ModuleScript* GetFetchedModuleScript(const KURL&) = 0;
 
   // https://html.spec.whatwg.org/#resolve-a-module-specifier
   static KURL ResolveModuleSpecifier(const String& module_request,
                                      const KURL& base_url);
 
   virtual ScriptModule CompileModule(const String& script,
                                      const String& url_str,
                                      AccessControlStatus) = 0;
 
   virtual ScriptValue InstantiateModule(ScriptModule) = 0;
 
   virtual Vector<String> ModuleRequestsFromScriptModule(ScriptModule) = 0;
 
  private:
   friend class ModuleMap;
 
   // Fetches a single module script.
   // This is triggered from fetchSingle() implementation (which is in ModuleMap)
   // if the cached entry doesn't exist.
   // The client can be notified either synchronously or asynchronously.
   virtual void FetchNewSingleModule(const ModuleScriptFetchRequest&,
                                     ModuleGraphLevel,
                                     ModuleScriptLoaderClient*) = 0;
 };
 
 }  // namespace blink
 
 #endif