Bug 1443925 - Part 3: Make nsScriptSecurityManager::GetStrictFileOriginPolicy threadsafe, r=ckerschb

This is used in various places in principals, as well as in the implementation
of nsScriptSecurityManager::SecurityCompareURIs which is also now threadsafe
after this change.

Differential Revision: https://phabricator.services.mozilla.com/D163033

caps/nsScriptSecurityManager.cpp

@@ -79,7 +79,7 @@ using namespace mozilla;
 using namespace mozilla::dom;
 
 nsIIOService* nsScriptSecurityManager::sIOService = nullptr;
-bool nsScriptSecurityManager::sStrictFileOriginPolicy = true;
+std::atomic<bool> nsScriptSecurityManager::sStrictFileOriginPolicy = true;
 
 namespace {
 

caps/nsScriptSecurityManager.h

@@ -134,7 +134,7 @@ class nsScriptSecurityManager final : public nsIScriptSecurityManager {
   // policy machinery will be removed soon.
   nsCOMPtr<nsIDomainPolicy> mDomainPolicy;
 
-  static bool sStrictFileOriginPolicy;
+  static std::atomic<bool> sStrictFileOriginPolicy;
 
   static nsIIOService* sIOService;
   static nsIStringBundle* sStrBundle;