Make file IO occur on the right thread.

chrome/browser/chromeos/system/timezone_settings.cc

Index: chrome/browser/chromeos/system/timezone_settings.cc
diff --git a/chrome/browser/chromeos/system/timezone_settings.cc b/chrome/browser/chromeos/system/timezone_settings.cc
index 03703a98fee07b975b5d8e7a1b35e4fbaf98ef5e..81aa03db1e3e017ca1a35d8ae48ce94e60b0b152 100644
--- a/chrome/browser/chromeos/system/timezone_settings.cc
+++ b/chrome/browser/chromeos/system/timezone_settings.cc
@@ -4,6 +4,7 @@
 
 #include "chrome/browser/chromeos/system/timezone_settings.h"
 
+#include "base/bind.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/logging.h"
@@ -12,6 +13,7 @@
 #include "base/memory/singleton.h"
 #include "base/string_util.h"
 #include "base/utf_string_conversions.h"
+#include "content/browser/browser_thread.h"
 
 namespace chromeos {
 namespace system {
@@ -120,7 +122,12 @@ void TimezoneSettingsImpl::SetTimezone(const icu::TimeZone& timezone) {
   std::string id;
   UTF16ToUTF8(unicode.getBuffer(), unicode.length(), &id);
   VLOG(1) << "Setting timezone to " << id;
-  SetTimezoneIDFromString(id);
+  // Change the timezone config files on the FILE thread. It's safe to do this
+  // in the background as the following operations don't depend on the
+  // completion of the config change.
+  BrowserThread::PostTask(BrowserThread::FILE,
+                          FROM_HERE,
+                          base::Bind(&SetTimezoneIDFromString, id));
   icu::TimeZone::setDefault(timezone);
   FOR_EACH_OBSERVER(Observer, observers_, TimezoneChanged(timezone));
 }