Backout bc20093cfc9d (bug 816656) for build failures during prepare-package

startupcache/StartupCache.cpp

@@ -139,9 +139,7 @@ StartupCache::~StartupCache()
   // but an early shutdown means either mTimer didn't run 
   // or the write thread is still running.
   WaitOnWriteThread();
-  // If we shutdown quickly timer wont have fired. Instead of writing
-  // it on the main thread and block the shutdown we simply wont update
-  // the startup cache.
+  WriteToDisk();
   gStartupCache = nullptr;
   (void)::NS_UnregisterMemoryReporter(mMappingMemoryReporter);
   (void)::NS_UnregisterMemoryReporter(mDataMemoryReporter);