Change files-ng cr-button ink color for ripple

Bug: 992823
Change-Id: I7de99801293d1fe2b25ba8e5a7f072f6f5014e28
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2053647
Commit-Queue: Alex Danilo <adanilo@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741264}

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

@@ -500,6 +500,7 @@ body[type='open-multi-file'].check-select .dialog-header {
 
 .dialog-header.files-ng cr-button {
   --hover-bg-color: rgba(0, 0, 0, 4%);
+  --ink-color: var(--google-grey-700);
   --text-color: currentColor;
 }