Fix sharesheet button typo in file_manager.css.

This CL fixes the sharesheet button type in file_manager.css.

BUG=1097623

Change-Id: I902164400191bafcefe09489129e2441dd0a2838
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2335851Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Maggie Cai <mxcai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796296}

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

@@ -800,7 +800,7 @@ body.check-select .dialog-header #share-menu-button > .icon {
   background-image: url(../images/files/ui/share.svg);
 }
 
-.dialog-header:not(.files-ng) #sharesheet-buttonn > .icon {
+.dialog-header:not(.files-ng) #sharesheet-button > .icon {
   background-image: -webkit-image-set(
       url(../images/files/ui/share_white.png) 1x,
       url(../images/files/ui/2x/share_white.png) 2x);