Print preview new: Fix scrolling in sidebar.

The lower part of the sidebar was incorrectly sized, causing the scrollbar
to appear after part of the content was already hidden.

Bug: 773928
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I50458546e67af9dfcd5416bdc81f6dfa7ca6e5b6
Reviewed-on: https://chromium-review.googlesource.com/775554Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517219}

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

@@ -22,13 +22,15 @@
       #sidebar {
         -webkit-border-end: 1px solid #c8c8c8;
         background-color: white;
+        display: flex;
+        flex-direction: column;
         width: 310px;
       }
 
       #settings {
         background: #fbfbfb;
         border-top: 1px solid #f3f3f3;
-        height: 100%;
+        flex: 1;
         overflow: auto;
       }