Use margins in ExtensionToolbarMenuView rather than laying out self

Currently, ExtensionToolbarMenuView sets its own position in
Layout(). This change sets the margins property instead, and modifies
MenuItemView::Layout to use this property.

Bug: 913998
Change-Id: Iab6305a0ad3dfc4fd936d17095ef6a65743e439c
Reviewed-on: https://chromium-review.googlesource.com/c/1393461
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Peter Boström <pbos@chromium.org>
Reviewed-by: Dana Fried <dfried@chromium.org>
Commit-Queue: Collin Baker <collinbaker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622190}
6 files changed