Ensure tests have an active task runner

chrome/browser/thumbnails/thumbnail_service_unittest.cc

Index: chrome/browser/thumbnails/thumbnail_service_unittest.cc
diff --git a/chrome/browser/thumbnails/thumbnail_service_unittest.cc b/chrome/browser/thumbnails/thumbnail_service_unittest.cc
index bdc2cf02a48665c6fc3f8765dedcd56b810ba526..075983a91370e6fae5c15a9442c038c0b09ef7ee 100644
--- a/chrome/browser/thumbnails/thumbnail_service_unittest.cc
+++ b/chrome/browser/thumbnails/thumbnail_service_unittest.cc
@@ -11,9 +11,12 @@
 #include "chrome/common/pref_names.h"
 #include "chrome/test/base/testing_profile.h"
 #include "components/history/core/browser/top_sites_impl.h"
+#include "content/public/test/test_browser_thread_bundle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-typedef testing::Test ThumbnailServiceTest;
+class ThumbnailServiceTest : public testing::Test {
+  content::TestBrowserThreadBundle thread_bundle_;
+};
 
 namespace {