Bug 1605248: Convert LoaderObserver::Clear to LoaderObserver::Disable; r=mhowell

We rename `LoaderObserver::Clear` to `LoaderObserver::Disable` to more accurately
reflect the following behaviour change:

Not only does the `Disable` call free any enqueued module load events, it also
ensures that no further module loads will be saved in the future. This reflects
the reality that any `mozglue` client that calls `Disable` has no intention of
ever processing these events.

Differential Revision: https://phabricator.services.mozilla.com/D57897

--HG--
extra : moz-landing-system : lando

mozglue/dllservices/LoaderObserver.cpp

@@ -80,6 +80,10 @@ void LoaderObserver::OnEndDllLoad(void* aContext, NTSTATUS aNtStatus,
 
   // No dll services, save for later
   AutoExclusiveLock lock(mLock);
+  if (!mEnabled) {
+    return;
+  }
+
   if (!mModuleLoads) {
     mModuleLoads = new ModuleLoadInfoVec();
   }
@@ -116,13 +120,14 @@ void LoaderObserver::Forward(detail::DllServicesBase* aNext) {
   delete moduleLoads;
 }
 
-void LoaderObserver::Clear() {
+void LoaderObserver::Disable() {
   ModuleLoadInfoVec* moduleLoads = nullptr;
 
   {  // Scope for lock
     AutoExclusiveLock lock(mLock);
     moduleLoads = mModuleLoads;
     mModuleLoads = nullptr;
+    mEnabled = false;
   }
 
   delete moduleLoads;

mozglue/dllservices/LoaderObserver.h

@@ -19,7 +19,7 @@ namespace glue {
 class MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS LoaderObserver final
     : public nt::LoaderObserver {
  public:
-  constexpr LoaderObserver() : mModuleLoads(nullptr) {}
+  constexpr LoaderObserver() : mModuleLoads(nullptr), mEnabled(true) {}
 
   void OnBeginDllLoad(void** aContext,
                       PCUNICODE_STRING aPreliminaryDllName) final;
@@ -31,11 +31,12 @@ class MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS LoaderObserver final
   void OnForward(ModuleLoadInfoVec&& aInfo) final;
 
   void Forward(mozilla::glue::detail::DllServicesBase* aSvc);
-  void Clear();
+  void Disable();
 
  private:
   Win32SRWLock mLock;
   ModuleLoadInfoVec* mModuleLoads;
+  bool mEnabled;
 };
 
 }  // namespace glue

mozglue/dllservices/WindowsDllBlocklist.cpp

@@ -769,5 +769,5 @@ MFBT_API void DllBlocklist_SetBasicDllServices(
   }
 
   aSvc->SetAuthenticodeImpl(GetAuthenticode());
-  gMozglueLoaderObserver.Clear();
+  gMozglueLoaderObserver.Disable();
 }