Revert of [ES6 modules] ModuleMap::GetFetchedModuleScript to return nullptr when entry not found / "fetching"

third_party/WebKit/Source/core/dom/ModuleMap.cpp

 // 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.
 
 #include "core/dom/ModuleMap.h"
 
 #include "core/dom/Modulator.h"
 #include "core/dom/ModuleScript.h"
 #include "core/loader/modulescript/ModuleScriptFetchRequest.h"
 #include "core/loader/modulescript/ModuleScriptLoaderClient.h"
@@ skipping 78 matching lines @@
   module_script_ = module_script;
   is_fetching_ = false;
 
   for (const auto& client : clients_) {
     DispatchFinishedNotificationAsync(client);
   }
   clients_.clear();
 }
 
 ModuleScript* ModuleMap::Entry::GetModuleScript() const {
+  DCHECK(!is_fetching_);
   return module_script_.Get();
 }
 
 ModuleMap::ModuleMap(Modulator* modulator) : modulator_(modulator) {
   DCHECK(modulator);
 }
 
 DEFINE_TRACE(ModuleMap) {
   visitor->Trace(map_);
   visitor->Trace(modulator_);
@@ skipping 29 matching lines @@
 
   // Step 3. If moduleMap[url] exists, asynchronously complete this algorithm
   // with moduleMap[url], and abort these steps.
   // Step 10. Set moduleMap[url] to module script, and asynchronously complete
   // this algorithm with module script.
   entry->AddClient(client);
 }
 
 ModuleScript* ModuleMap::GetFetchedModuleScript(const KURL& url) const {
   MapImpl::const_iterator it = map_.find(url);
-  if (it == map_.end())
-    return nullptr;
+  CHECK_NE(it, map_.end());
   return it->value->GetModuleScript();
 }
 
 }  // namespace blink