Temporary whitelist several cases of disk I/O on the UI threads in cros.

base/nss_util.cc

Index: base/nss_util.cc
diff --git a/base/nss_util.cc b/base/nss_util.cc
index 8e250c41c7b801f9e07452a6de42a91a271e136a..fe78fe0c218bfb37162702f2cf6b5815b52cbe41 100644
--- a/base/nss_util.cc
+++ b/base/nss_util.cc
@@ -165,6 +165,9 @@ class NSSInitSingleton {
 #if defined(OS_CHROMEOS)
   void OpenPersistentNSSDB() {
     if (!chromeos_user_logged_in_) {
+      // GetDefaultConfigDirectory causes us to do blocking IO on UI thread.
+      // Temporarily allow it until we fix http://crbug.com.70119
+      ThreadRestrictions::ScopedAllowIO allow_io;
       chromeos_user_logged_in_ = true;
       real_db_slot_ = OpenUserDB(GetDefaultConfigDirectory(),
                                  "Real NSS database");