Bug 1432901 - Part 12: Break cycles manually during shutdown r=yulia

Since mozJSComponentLoader is destroyed after the cycle collector, we need to
break cycles manually before the final cycle collection otherwise we get a
memory leak. Unload() is called at an appropriate earlier point in shutdown.

Differential Revision: https://phabricator.services.mozilla.com/D145567

js/loader/ModuleLoaderBase.cpp

@@ -873,6 +873,14 @@ ModuleLoaderBase::~ModuleLoaderBase() {
   LOG(("ModuleLoaderBase::~ModuleLoaderBase %p", this));
 }
 
+void ModuleLoaderBase::Shutdown() {
+  MOZ_ASSERT(mFetchingModules.IsEmpty());
+  mFetchedModules.Clear();
+  mGlobalObject = nullptr;
+  mEventTarget = nullptr;
+  mLoader = nullptr;
+}
+
 bool ModuleLoaderBase::HasPendingDynamicImports() const {
   return !mDynamicImportRequests.isEmpty();
 }

js/loader/ModuleLoaderBase.h

@@ -180,6 +180,9 @@ class ModuleLoaderBase : public nsISupports {
                             nsISerialEventTarget* aEventTarget =
                                 mozilla::GetMainThreadSerialEventTarget());
 
+  // Called to break cycles during shutdown to prevent memory leaks.
+  void Shutdown();
+
   using LoadedScript = JS::loader::LoadedScript;
   using ScriptFetchOptions = JS::loader::ScriptFetchOptions;
   using ScriptLoadRequest = JS::loader::ScriptLoadRequest;

js/xpconnect/loader/mozJSComponentLoader.cpp

@@ -475,6 +475,11 @@ void mozJSComponentLoader::InitStatics() {
 void mozJSComponentLoader::Unload() {
   if (sSelf) {
     sSelf->UnloadModules();
+
+    if (sSelf->mModuleLoader) {
+      sSelf->mModuleLoader->Shutdown();
+      sSelf->mModuleLoader = nullptr;
+    }
   }
 }