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 f94a4a87e526b63831af0a6b95836441d09b4ccf..ae775ffeedd63ebd09540d69296cd0a08d470c74 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;
@@ -295,6 +251,10 @@ div.splitter {
   position: absolute;
   right: 0;
   top: 0;
+
+  /* TODO(yamaguchi): Remove these when crbug.com/671644 is resolved. */
+  background-color: rgb(250, 250, 250);
+  contain: paint;
 }
 
 #directory-tree .tree-row {
@@ -1145,9 +1105,9 @@ html[dir='rtl'] .breadcrumbs .separator {
 }
 
 #file-list {
-  /* Override overflow specifying by table_list.js to use the original scroll
-     bar. crbug.com/391698 */
-  overflow: scroll !important;
+  /* TODO(yamaguchi): Remove these when crbug.com/671644 is resolved. */
+  background-color: rgb(250, 250, 250);
+  contain: paint;
 }
 
 #file-list .drag-selection-border {