Add tooltips to the header buttons in Files app.

chrome/browser/chromeos/file_manager/file_manager_jstest.cc

Index: chrome/browser/chromeos/file_manager/file_manager_jstest.cc
diff --git a/chrome/browser/chromeos/file_manager/file_manager_jstest.cc b/chrome/browser/chromeos/file_manager/file_manager_jstest.cc
index 281d54310970251d31bf76552e143ec6eec7b4dc..8b6a347b34f4f885e3943dce886d008a1d396bdb 100644
--- a/chrome/browser/chromeos/file_manager/file_manager_jstest.cc
+++ b/chrome/browser/chromeos/file_manager/file_manager_jstest.cc
@@ -173,3 +173,8 @@ IN_PROC_BROWSER_TEST_F(FileManagerJsTest, ProvidersModel) {
   RunTest(base::FilePath(
       FILE_PATH_LITERAL("foreground/js/providers_model_unittest.html")));
 }
+
+IN_PROC_BROWSER_TEST_F(FileManagerJsTest, TooltipController) {
+  RunTest(base::FilePath(
+      FILE_PATH_LITERAL("foreground/js/tooltip_controller_unittest.html")));
+}