Bug 1173573 - Fix possible crash initializing sessionstorage. r=honzab

dom/storage/DOMStorageCache.cpp

@@ -771,8 +771,11 @@ DOMStorageCache::StartDatabase()
 
     sDatabase = db.forget();
   } else {
+    // Use DOMLocalStorageManager::Ensure in case we're called from
+    // DOMSessionStorageManager's initializer and we haven't yet initialized the
+    // local storage manager.
     nsRefPtr<DOMStorageDBChild> db = new DOMStorageDBChild(
-        DOMLocalStorageManager::Self());
+        DOMLocalStorageManager::Ensure());
 
     nsresult rv = db->Init();
     if (NS_FAILED(rv)) {

dom/storage/DOMStorageManager.cpp

@@ -628,6 +628,21 @@ DOMLocalStorageManager::~DOMLocalStorageManager()
   sSelf = nullptr;
 }
 
+DOMLocalStorageManager*
+DOMLocalStorageManager::Ensure()
+{
+  if (sSelf) {
+    return sSelf;
+  }
+
+  // Cause sSelf to be populated.
+  nsCOMPtr<nsIDOMStorageManager> initializer =
+    do_GetService("@mozilla.org/dom/localStorage-manager;1");
+  MOZ_ASSERT(sSelf, "Didn't initialize?");
+
+  return sSelf;
+}
+
 // DOMSessionStorageManager
 
 DOMSessionStorageManager::DOMSessionStorageManager()

dom/storage/DOMStorageManager.h

@@ -126,6 +126,9 @@ public:
   // Global getter of localStorage manager service
   static DOMLocalStorageManager* Self() { return sSelf; }
 
+  // Like Self, but creates an instance if we're not yet initialized.
+  static DOMLocalStorageManager* Ensure();
+
 private:
   static DOMLocalStorageManager* sSelf;
 };