Make contents of the Feedback sys info window selectable and copyable

BUG=838561

Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I7c4874880c80706327d97cbf86cef54c940abd6b
Reviewed-on: https://chromium-review.googlesource.com/1040348Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555509}

chrome/browser/resources/feedback/css/sys_info.css

@@ -5,6 +5,7 @@
 html,
 body {
   overflow: visible;
+  user-select: auto;
 }
 
 #detailsTable {