ThreadRestrictions: disallow blocking IO on the UI thread

chrome/browser/browser_shutdown.cc

Index: chrome/browser/browser_shutdown.cc
diff --git a/chrome/browser/browser_shutdown.cc b/chrome/browser/browser_shutdown.cc
index 98e0af7440ad88c6c04533337ba822b098282556..8f1fb80366cf22f8a9b39826e81e261ea443776f 100644
--- a/chrome/browser/browser_shutdown.cc
+++ b/chrome/browser/browser_shutdown.cc
@@ -16,6 +16,7 @@
 #include "base/string_number_conversions.h"
 #include "base/string_util.h"
 #include "base/thread.h"
+#include "base/thread_restrictions.h"
 #include "base/time.h"
 #include "build/build_config.h"
 #include "chrome/browser/about_flags.h"
@@ -100,6 +101,12 @@ FilePath GetShutdownMsPath() {
 }
 
 void Shutdown() {
+  // During shutdown we will end up some blocking operations.  But the
+  // work needs to get done and we're going to wait for them no matter
+  // what thread they're on, so don't worry about it slowing down
+  // shutdown.
+  base::ThreadRestrictions::SetIOAllowed(true);
+
   // Unload plugins. This needs to happen on the IO thread.
   BrowserThread::PostTask(
         BrowserThread::IO, FROM_HERE,