Print Preview Componentization: Make text non-selectable

Bug: 846493
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I6d7634edabe8e756ac7ea62fc88d223902f9a46f
Reviewed-on: https://chromium-review.googlesource.com/1072696Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561938}

chrome/browser/resources/print_preview/new/app.html

@@ -40,6 +40,7 @@
       :host {
         display: flex;
         height: 100%;
+        user-select: none;
       }
 
       #sidebar {