Print Preview Duplex Dropdown: Tweak icon position and size

Increasing side padding to 8px from 4px, and decreasing icon size from
20px to 16px, per UX input.

Bug: 934061
Change-Id: Iab5761e7be3b5933a4481200a4de2f07b1f72c58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1540068Reviewed-by: Esmael El-Moslimany <aee@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644511}

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

@@ -16,8 +16,8 @@
   <template>
     <style include="print-preview-shared cr-hidden-style md-select">
       :host {
-        --duplex-icon-side-padding: 4px;
-        --duplex-icon-size: 20px;
+        --duplex-icon-side-padding: 8px;
+        --duplex-icon-size: 16px;
       }
 
       .md-select {