Add an additional pixel to the attached bookmarks bar.

BOOKMARK_BAR_HEIGHT gives the height of the bookmark when attached so
giving an additional pixel here to the vertical margin of the bookmark
bar.
This makes it so there are the same number of pixels above and below
each button on the bookmarks bar when the bookmark is attached.

Bug: 865555
Change-Id: I271bfb7f48ef2faa390a8c9ae595c165dbc0bde9
Reviewed-on: https://chromium-review.googlesource.com/c/1280928Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Commit-Queue: Charlene Yan <cyan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603707}

chrome/browser/ui/layout_constants.cc

@@ -32,7 +32,9 @@ int GetLayoutConstant(LayoutConstant constant) {
     case BOOKMARK_BAR_HEIGHT:
       // The fixed margin ensures the bookmark buttons appear centered relative
       // to the white space above and below.
-      return GetLayoutConstant(BOOKMARK_BAR_BUTTON_HEIGHT) + 4;
+      static constexpr int kBookmarkBarAttachedVerticalMargin = 5;
+      return GetLayoutConstant(BOOKMARK_BAR_BUTTON_HEIGHT) +
+             kBookmarkBarAttachedVerticalMargin;
     case BOOKMARK_BAR_BUTTON_HEIGHT:
       return touch_ui ? 36 : 28;
     case BOOKMARK_BAR_NTP_HEIGHT: