Bug 1942014 - QM: Add a new environment variable for enabling incremental origin initialization; r=dom-storage-reviewers,hsingh

- Updated QuotaPrefs::IncrementalOriginInitializationEnabled to check for the
  environment variable MOZ_ENABLE_INC_ORIGIN_INIT.
- If the environment variable is set to 1, it enables incremental origin
  initialization regardless of the preference value.
- Retained the existing behavior of using the
  dom.quotaManager.temporaryStorage.incrementalOriginInitialization preference
  as the primary configuration.
- The environment variable is primarily intended for use in testing
  infrastructure and harnesses

Differential Revision: https://phabricator.services.mozilla.com/D234578

dom/quota/QuotaPrefs.cpp

@@ -7,6 +7,7 @@
 #include "QuotaPrefs.h"
 
 #include "mozilla/StaticPrefs_dom.h"
+#include "prenv.h"
 
 // The STATIC_PREF macro helps avoid lines exceeding 80 characters due to
 // long method names generated from StaticPrefList.yaml. It constructs
@@ -32,8 +33,13 @@ bool QuotaPrefs::TriggerOriginInitializationInBackgroundEnabled() {
 
 // static
 bool QuotaPrefs::IncrementalOriginInitializationEnabled() {
-  return STATIC_PREF(dom, quotaManager, temporaryStorage,
-                     incrementalOriginInitialization)();
+  if (STATIC_PREF(dom, quotaManager, temporaryStorage,
+                  incrementalOriginInitialization)()) {
+    return true;
+  }
+
+  const char* env = PR_GetEnv("MOZ_ENABLE_INC_ORIGIN_INIT");
+  return (env && *env == '1');
 }
 
 }  // namespace mozilla::dom::quota