Don't display customize button on non-google NTP.

Bug: 938240
Change-Id: Ia75d55ba64415fa8c77f28326afd01ca2861e9d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504267Reviewed-by: Kyle Milka <kmilka@chromium.org>
Commit-Queue: Gayane Petrosyan <gayane@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637966}

chrome/browser/resources/local_ntp/custom_backgrounds.css

@@ -59,6 +59,10 @@ html[dir=rtl] #edit-bg {
   right: auto;
 }
 
+.non-google-page #edit-bg {
+  display: none;
+}
+
 #edit-bg-icon {
   -webkit-mask-image: url(icons/icon_pencil.svg);
   -webkit-mask-position-x: center;