Unpack theme data from extensions off of UI thread.

chrome/browser/sync/test/integration/sync_integration_test_util.h

Index: chrome/browser/sync/test/integration/sync_integration_test_util.h
diff --git a/chrome/browser/sync/test/integration/sync_integration_test_util.h b/chrome/browser/sync/test/integration/sync_integration_test_util.h
index c3af2d76cbceb07419832d9dc463e25eb6e2e4b1..63df4c976f76ffbbf2f508105d7f99eb4ff06c6a 100644
--- a/chrome/browser/sync/test/integration/sync_integration_test_util.h
+++ b/chrome/browser/sync/test/integration/sync_integration_test_util.h
@@ -11,10 +11,15 @@
 #include "chrome/browser/sync/test/integration/single_client_status_change_checker.h"
 #include "components/sync/base/model_type.h"
 
+class Profile;
+
 namespace browser_sync {
 class ProfileSyncService;
 }  // namespace browser_sync
 
+// Sets a custom theme and wait until the asynchronous process is done.
+void SetCustomTheme(Profile* profile, int theme_index = 0);
+
 // Checker to block until the server has a given number of entities.
 class ServerCountMatchStatusChecker
     : public fake_server::FakeServerMatchStatusChecker {