[directorytree] Do not filter FSP icons in files-ng

The iconSet property of most volume types is empty, but we expect that
third party volumes (ANDROID_FILES, DOCUMENT_PROVIDERS and File System
Providers) should provide icons in their iconSets.

File System Providers icons are filtered via CSS, to try and create an
"active" state icon for their directory tree tab [1].

The filtered icon can have poor visual quality, depending on the icon,
but ANDROID_FILES, DOCUMENT_PROVIDERS icons are left alone - we do not
try and filter them. Make File System Providers join the party, do not
try and filter them either.

[1] iconsSets do not provide "active" icon variants.

Bug: 992819
Change-Id: I675f465d25ac45afdb669657d3a22c24a02ecf17
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2094516Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748097}

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

@@ -818,12 +818,6 @@ body.files-ng [file-type-icon='removable'] {
   filter: contrast(0) brightness(0.7143);
 }
 
-.tree-row:not([active]) > .file-row > [volume-type-icon='provided'] {
-  /* Third-party icons are not provided with both an active and a non-active
-  version. This filter defines the non-active version of a provided icon. */
-  filter: contrast(0) brightness(0.85);
-}
-
 [root-type-icon='recent'] {
   background-image: -webkit-image-set(
       url(../images/volumes/recent.png) 1x,