Revert of [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 f5e15a513c5b63fa00ea937407b0c4897aa9da42..ea685c364e41b72adcecbe5c4afa28caeeee8a35 100644
--- a/third_party/WebKit/Source/core/dom/ModuleMap.cpp
+++ b/third_party/WebKit/Source/core/dom/ModuleMap.cpp
@@ -96,6 +96,7 @@
 }
 
 ModuleScript* ModuleMap::Entry::GetModuleScript() const {
+  DCHECK(!is_fetching_);
   return module_script_.Get();
 }
 
@@ -145,8 +146,7 @@
 
 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();
 }