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

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

Index: third_party/WebKit/Source/core/dom/ModuleMap.cpp
diff --git a/third_party/WebKit/Source/core/dom/ModuleMap.cpp b/third_party/WebKit/Source/core/dom/ModuleMap.cpp
index ea685c364e41b72adcecbe5c4afa28caeeee8a35..f5e15a513c5b63fa00ea937407b0c4897aa9da42 100644
--- a/third_party/WebKit/Source/core/dom/ModuleMap.cpp
+++ b/third_party/WebKit/Source/core/dom/ModuleMap.cpp
@@ -96,7 +96,6 @@ void ModuleMap::Entry::NotifyNewSingleModuleFinished(
 }
 
 ModuleScript* ModuleMap::Entry::GetModuleScript() const {
-  DCHECK(!is_fetching_);
   return module_script_.Get();
 }
 
@@ -146,7 +145,8 @@ void ModuleMap::FetchSingleModuleScript(const ModuleScriptFetchRequest& request,
 
 ModuleScript* ModuleMap::GetFetchedModuleScript(const KURL& url) const {
   MapImpl::const_iterator it = map_.find(url);
-  CHECK_NE(it, map_.end());
+  if (it == map_.end())
+    return nullptr;
   return it->value->GetModuleScript();
 }