Bug 1611651 - Add pref for stale-while-revalidate r=dragana

Differential Revision: https://phabricator.services.mozilla.com/D65813

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

modules/libpref/init/StaticPrefList.yaml

@@ -7366,6 +7366,11 @@
   value: true
   mirror: always
 
+- name: network.http.stale_while_revalidate.enabled
+  type: RelaxedAtomicBool
+  value: true
+  mirror: always
+
 # Single TRR request timeout, in milliseconds
 - name: network.trr.request_timeout_ms
   type: RelaxedAtomicUint32

netwerk/protocol/http/nsHttp.cpp

@@ -423,7 +423,8 @@ bool ValidationRequired(bool isForcedValid,
     LOG(("  not validating, expire time not in the past"));
   } else if (cachedResponseHead->MustValidateIfExpired()) {
     doValidation = true;
-  } else if (cachedResponseHead->StaleWhileRevalidate(now, expiration)) {
+  } else if (cachedResponseHead->StaleWhileRevalidate(now, expiration) &&
+             StaticPrefs::network_http_stale_while_revalidate_enabled()) {
     LOG(("  not validating, in the stall-while-revalidate window"));
     doValidation = false;
     if (performBackgroundRevalidation) {

netwerk/protocol/http/nsHttpChannel.cpp

@@ -10569,6 +10569,10 @@ NS_IMPL_ISUPPORTS(BackgroundRevalidatingListener, nsIStreamListener,
 }  // namespace
 
 void nsHttpChannel::PerformBackgroundCacheRevalidation() {
+  if (!StaticPrefs::network_http_stale_while_revalidate_enabled()) {
+    return;
+  }
+
   LOG(("nsHttpChannel::PerformBackgroundCacheRevalidation %p", this));
 
   Unused << NS_DispatchToMainThreadQueue(