Bug 1356686: Put OMT decompression behind a pref r=necko-reviewers,valentin

Differential Revision: https://phabricator.services.mozilla.com/D204957

modules/libpref/init/StaticPrefList.yaml

@@ -13285,6 +13285,11 @@
   value: "file,moz-gio"
   mirror: never
 
+# Enable off-main-thread decompression of network streams
+- name: network.decompression_off_mainthread
+  type: bool
+  value: true
+  mirror: always
 
 #---------------------------------------------------------------------------
 # Prefs starting with "nglayout."

netwerk/streamconv/converters/nsHTTPCompressConv.cpp

@@ -137,7 +137,9 @@ nsHTTPCompressConv::MaybeRetarget(nsIRequest* request) {
   if (!req) {
     return NS_ERROR_NO_INTERFACE;
   }
-
+  if (!StaticPrefs::network_decompression_off_mainthread()) {
+    return NS_OK;
+  }
   nsCOMPtr<nsISerialEventTarget> target;
   rv = req->GetDeliveryTarget(getter_AddRefs(target));
   if (NS_FAILED(rv) || !target || target->IsOnCurrentThread()) {