Disallow UI/IO thread blocking on any other thread.

chrome/browser/metrics/metrics_service.cc

Index: chrome/browser/metrics/metrics_service.cc
===================================================================
--- chrome/browser/metrics/metrics_service.cc	(revision 133458)
+++ chrome/browser/metrics/metrics_service.cc	(working copy)
@@ -152,6 +152,7 @@
 #include "base/string_number_conversions.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/thread.h"
+#include "base/threading/thread_restrictions.h"
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/browser/bookmarks/bookmark_model.h"
@@ -1438,6 +1439,8 @@
   base::WaitableEvent done_writing(false, false);
   BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
                           base::Bind(Signal, &done_writing));
+  // http://crbug.com/124954
+  base::ThreadRestrictions::ScopedAllowWait allow_wait;
   done_writing.TimedWait(base::TimeDelta::FromHours(1));
 
   // Redundant setting to assure that we always reset this value at shutdown