Don't clear session when "clear on shutdown" is set if we're actually just doing a restart. b=487219 r=zeniko

browser/components/sessionstore/src/nsSessionStore.js

@@ -326,8 +326,10 @@ SessionStoreService.prototype = {
       this._loadState = STATE_QUITTING;
       break;
     case "quit-application":
-      if (aData == "restart")
+      if (aData == "restart") {
         this._prefBranch.setBoolPref("sessionstore.resume_session_once", true);
+        this._clearingOnShutdown = false;
+      }
       this._loadState = STATE_QUITTING; // just to be sure
       this._uninit();
       break;