Add a do_not_sync pref to ExtensionPrefs.

chrome/browser/extensions/extension_util.cc

Index: chrome/browser/extensions/extension_util.cc
diff --git a/chrome/browser/extensions/extension_util.cc b/chrome/browser/extensions/extension_util.cc
index dd28913209f58be2934b1f20c15c4b18276edda1..45dc7408cc3cda2f8d46ea09561abce570b7bf7a 100644
--- a/chrome/browser/extensions/extension_util.cc
+++ b/chrome/browser/extensions/extension_util.cc
@@ -180,9 +180,16 @@ bool IsAppLaunchableWithoutEnabling(const std::string& extension_id,
       extension_id, ExtensionRegistry::ENABLED) != NULL;
 }
 
+bool ShouldSyncExtension(const Extension* extension,
+                         content::BrowserContext* context) {
+  return sync_helper::IsSyncableExtension(extension) &&
+         !ExtensionPrefs::Get(context)->DoNotSync(extension->id());
+}
+
 bool ShouldSyncApp(const Extension* app, content::BrowserContext* context) {
   return sync_helper::IsSyncableApp(app) &&
-      !util::IsEphemeralApp(app->id(), context);
+         !util::IsEphemeralApp(app->id(), context) &&
+         !ExtensionPrefs::Get(context)->DoNotSync(app->id());
 }
 
 bool IsExtensionIdle(const std::string& extension_id,