When searching show spinner inplace of magnifying glass in the searchbox.

chrome/browser/resources/file_manager/css/file_manager.css

Index: chrome/browser/resources/file_manager/css/file_manager.css
diff --git a/chrome/browser/resources/file_manager/css/file_manager.css b/chrome/browser/resources/file_manager/css/file_manager.css
index 1985115c40aa847aa1e9dece276908d29b927d19..36df53d04a5f55d70cae53ff8a6ed7cfbc90dd17 100644
--- a/chrome/browser/resources/file_manager/css/file_manager.css
+++ b/chrome/browser/resources/file_manager/css/file_manager.css
@@ -463,6 +463,11 @@ div.root-eject:hover {
   width: 150px;
 }
 
+.searching #search-box {
+  background-image: url('../images/common/spinner.svg');
+  background-size: 17px 17px;
+}
+
 #search-box:focus {
   border-color: rgb(77, 144, 254);
   outline: none;