Bug 1550108 - Reduce stack size on StartupCache threads r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D46225

--HG--
extra : moz-landing-system : lando

Author: squarewave

startupcache/StartupCache.cpp

@@ -251,7 +251,7 @@ void StartupCache::StartPrefetchMemoryThread() {
   // barring a coordinated global scheduling system this is the best we get.
   mPrefetchThread = PR_CreateThread(
       PR_USER_THREAD, StartupCache::ThreadedPrefetch, this, PR_PRIORITY_NORMAL,
-      PR_GLOBAL_THREAD, PR_JOINABLE_THREAD, 0);
+      PR_GLOBAL_THREAD, PR_JOINABLE_THREAD, 256 * 1024);
 }
 
 /**
@@ -694,7 +694,7 @@ void StartupCache::WriteTimeout(nsITimer* aTimer, void* aClosure) {
   startupCacheObj->mCacheData.reset();
   startupCacheObj->mWriteThread = PR_CreateThread(
       PR_USER_THREAD, StartupCache::ThreadedWrite, startupCacheObj,
-      PR_PRIORITY_NORMAL, PR_GLOBAL_THREAD, PR_JOINABLE_THREAD, 0);
+      PR_PRIORITY_NORMAL, PR_GLOBAL_THREAD, PR_JOINABLE_THREAD, 256 * 1024);
 }
 
 // We don't want to refcount StartupCache, so we'll just