Bug 1599569 - Make nsScriptSecurityManager::ClearJSCallbacks into a static method. r=kmag

XPConnect calls this method during shutdown after the pointer to the
singleton nsScriptSecurityManager has been cleared, so it is actually
calling it with a null |this|. Nobody noticed this because it isn't
actually using |this|. This patch turns it into a static method to
make the sanitizers happy.

Differential Revision: https://phabricator.services.mozilla.com/D54846

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

caps/nsScriptSecurityManager.cpp

@@ -1389,6 +1389,7 @@ void nsScriptSecurityManager::InitJSCallbacks(JSContext* aCx) {
   JS_SetTrustedPrincipals(aCx, BasePrincipal::Cast(mSystemPrincipal));
 }
 
+/* static */
 void nsScriptSecurityManager::ClearJSCallbacks(JSContext* aCx) {
   JS_SetSecurityCallbacks(aCx, nullptr);
   JS_SetTrustedPrincipals(aCx, nullptr);

caps/nsScriptSecurityManager.h

@@ -52,7 +52,9 @@ class nsScriptSecurityManager final : public nsIScriptSecurityManager {
   static void InitStatics();
 
   void InitJSCallbacks(JSContext* aCx);
-  void ClearJSCallbacks(JSContext* aCx);
+
+  // This has to be static because it is called after gScriptSecMan is cleared.
+  static void ClearJSCallbacks(JSContext* aCx);
 
   static already_AddRefed<mozilla::SystemPrincipal>
   SystemPrincipalSingletonConstructor();

js/xpconnect/src/XPCJSRuntime.cpp

@@ -1121,7 +1121,7 @@ void XPCJSRuntime::Shutdown(JSContext* cx) {
 
   JS::SetGCSliceCallback(cx, mPrevGCSliceCallback);
 
-  nsScriptSecurityManager::GetScriptSecurityManager()->ClearJSCallbacks(cx);
+  nsScriptSecurityManager::ClearJSCallbacks(cx);
 
   // Shut down the helper threads
   gHelperThreads->Shutdown();