Bug 1641874 - Make the pref unchangeable at runtime; r=nika

Differential Revision: https://phabricator.services.mozilla.com/D78282

docshell/base/BrowsingContext.cpp

@@ -1022,7 +1022,8 @@ RefPtr<SessionStorageManager> BrowsingContext::GetSessionStorageManager() {
 bool BrowsingContext::CrossOriginIsolated() {
   MOZ_ASSERT(NS_IsMainThread());
 
-  return StaticPrefs::dom_postMessage_sharedArrayBuffer_withCOOP_COEP() &&
+  return StaticPrefs::
+             dom_postMessage_sharedArrayBuffer_withCOOP_COEP_AtStartup() &&
          Top()->GetOpenerPolicy() ==
              nsILoadInfo::
                  OPENER_POLICY_SAME_ORIGIN_EMBEDDER_POLICY_REQUIRE_CORP &&

dom/base/Document.cpp

@@ -8079,7 +8079,8 @@ void Document::SetDomain(const nsAString& aDomain, ErrorResult& rv) {
     return;
   }
 
-  if (StaticPrefs::dom_postMessage_sharedArrayBuffer_withCOOP_COEP() &&
+  if (StaticPrefs::
+          dom_postMessage_sharedArrayBuffer_withCOOP_COEP_AtStartup() &&
       GetBrowsingContext() && GetBrowsingContext()->CrossOriginIsolated()) {
     WarnOnceAbout(Document::eDocumentSetDomainNotAllowed);
     return;

dom/workers/WorkerPrivate.cpp

@@ -5244,7 +5244,8 @@ bool WorkerPrivate::IsSharedMemoryAllowed() const {
 }
 
 bool WorkerPrivate::CrossOriginIsolated() const {
-  if (!StaticPrefs::dom_postMessage_sharedArrayBuffer_withCOOP_COEP()) {
+  if (!StaticPrefs::
+          dom_postMessage_sharedArrayBuffer_withCOOP_COEP_AtStartup()) {
     return false;
   }
 

modules/libpref/init/StaticPrefList.yaml

@@ -2227,13 +2227,13 @@
 # re-SAB: Whether to allow postMessage of a SharedArrayBuffer if various
 # preconditions related to COOP and COEP are met
 - name: dom.postMessage.sharedArrayBuffer.withCOOP_COEP
-  type: RelaxedAtomicBool
+  type: bool
 #if !defined(ANDROID)
   value: @IS_NIGHTLY_BUILD@
 #else
   value: false # Blocked by DocumentChannel, see Bug 1589982.
 #endif
-  mirror: always
+  mirror: once
 
 # Overridden in all.js on RELEASE_OR_BETA in order to add the locked attribute.
 - name: dom.postMessage.sharedArrayBuffer.bypassCOOP_COEP.insecure.enabled