MD Settings: Center icons in navigation menu.

Bug: 730904
Change-Id: Id37a8a9c5d9e7ec5d5112ad2567a6c376c6e591e
Reviewed-on: https://chromium-review.googlesource.com/567332Reviewed-by: Dave Schuyler <dschuyler@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485848}

chrome/browser/resources/settings/settings_menu/settings_menu.html

@@ -26,6 +26,7 @@
         -webkit-margin-end: 2px;  /* Margin so selected outline is visible. */
         -webkit-margin-start: 1px;
         -webkit-padding-start: 23px;  /* 24px - 1px from margin for outline. */
+        align-items: center;
         color: var(--settings-nav-grey);
         display: flex;
         font-weight: 500;