Replace homebrew scrollbar in Files app with that of Blink.

ui/file_manager/file_manager/foreground/css/file_manager.css

Index: ui/file_manager/file_manager/foreground/css/file_manager.css
diff --git a/ui/file_manager/file_manager/foreground/css/file_manager.css b/ui/file_manager/file_manager/foreground/css/file_manager.css
index 7c33b84b227f4f15eaf7977ffb9ca5f00e7a6136..4f6b8285cc0a2040624090e21f1f07deaf1087df 100644
--- a/ui/file_manager/file_manager/foreground/css/file_manager.css
+++ b/ui/file_manager/file_manager/foreground/css/file_manager.css
@@ -60,50 +60,6 @@ a:focus {
   opacity: 0.8;
 }
 
-.dialog-container ::-webkit-scrollbar {
-  height: 0;
-  width: 0;
-}
-
-/* TODO(mtomasz): Flip scrollbars to the opposite side for RTL languages. */
-.scrollbar-vertical {
-  bottom: 0;
-  flex: none;
-  pointer-events: none;
-  position: absolute;
-  right: 0;
-  top: 0;
-  width: 10px;
-  z-index: 500;  /* Must be below the contextmenu (600). */
-}
-
-.scrollbar-button {
-  background-color: black;
-  border-radius: 3px;
-  border: 1px solid #ccc;
-  box-sizing: border-box;
-  height: 50%;
-  margin-right: 2px;
-  opacity: 0;
-  pointer-events: auto;
-  position: absolute;
-  transition: opacity 100ms;
-  width: 8px;
-}
-
-:hover > .scrollbar-vertical > .scrollbar-button,
-.scrollbar-vertical > .scrollbar-button.scrolling {
-  opacity: 0.3;
-}
-
-.scrollbar-vertical > .scrollbar-button:hover {
-  opacity: 0.4;
-}
-
-.scrollbar-vertical > .scrollbar-button.pressed {
-  opacity: 0.5;
-}
-
 /* Main part of the dialog between header and footer. */
 .dialog-container {
   align-items: stretch;
@@ -1003,12 +959,6 @@ html[dir='rtl'] .breadcrumbs .separator {
   flex: auto;
 }
 
-#file-list {
-  /* Override overflow specifying by table_list.js to use the original scroll
-     bar. crbug.com/391698 */
-  overflow: scroll !important;
-}
-
 #file-list .drag-selection-border {
   -webkit-box-sizing: border-box;
   background-color: rgba(255, 255, 255, 0.3);