Disable synchronous XMLHttpRequests in platform app documents.

chrome/browser/extensions/extension_webkit_preferences.cc

Index: chrome/browser/extensions/extension_webkit_preferences.cc
diff --git a/chrome/browser/extensions/extension_webkit_preferences.cc b/chrome/browser/extensions/extension_webkit_preferences.cc
index 14fbbbef232fa607929badc1c9ea05831d62b85e..b15f33988cead6e5897f6211faf39546b2ccecfa 100644
--- a/chrome/browser/extensions/extension_webkit_preferences.cc
+++ b/chrome/browser/extensions/extension_webkit_preferences.cc
@@ -38,6 +38,7 @@ void SetPreferences(const extensions::Extension* extension,
   if (extension->is_platform_app()) {
     webkit_prefs->databases_enabled = false;
     webkit_prefs->local_storage_enabled = false;
+    webkit_prefs->sync_xhr_in_documents_enabled = false;
   }
 
   // Enable WebGL features that regular pages can't access, since they add