Bug 1011487 - HTTP cache v2: WalkCacheRunnable may release it's callback on a non-main thread, r=michal

netwerk/cache2/CacheStorageService.cpp

@@ -179,6 +179,14 @@ protected:
     , mNotifyStorage(true)
     , mVisitEntries(aVisitEntries)
   {
+    MOZ_ASSERT(NS_IsMainThread());
+  }
+
+  virtual ~WalkCacheRunnable()
+  {
+    if (mCallback) {
+      ProxyReleaseMainThread(mCallback);
+    }
   }
 
   nsRefPtr<CacheStorageService> mService;