[directorytree] Make tab hover color G Grey 100

The tab hover color was visually too dark G Grey 200 (should be 100).

Bug: 992819
Change-Id: I96c02a72fc4d23ec0a3bb7981ed4429de4ef0210
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2094580Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Alex Danilo <adanilo@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748147}

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

@@ -305,7 +305,7 @@ html[dir='rtl'] #directory-tree .tree-row > .file-row {
 
 html:not(.col-resize) #directory-tree
     .tree-row:not([active]):not([selected]):hover > .file-row {
-  background-color: var(--google-grey-200);
+  background-color: var(--google-grey-100);
 }
 
 #directory-tree:focus .tree-row[selected] > .file-row {