Sync Confirmation: add padding for heading.

Screenshot after fix: https://imgur.com/a/0C7ZNai

This CL adds padding for the sync-confirmation title so the text doesn't
go right up to the edge, since that looks pretty broken.

Bug: 868090
Change-Id: I7d842068860abe9886c2cfe77af1ca1f48440b85
Reviewed-on: https://chromium-review.googlesource.com/1153555Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Scott Chen <scottchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579120}

chrome/browser/resources/signin/dice_sync_confirmation/sync_confirmation_app.html

@@ -77,6 +77,7 @@
         color: var(--paper-grey-800);
         font-weight: normal;
         margin-bottom: 32px;
+        padding: 0 24px;
         text-align: center;
       }