Tweak message header actions.

Once again, I missed an asset in the drop, since there is actually a
sepcialized one for the message view.

Also, use styles to fill out the entire height to the header to make the
touch targets bigger, as consistent with Gmail.

Bug: 5290357
Change-Id: I6754b3ef986dbf57c7c68bc595cf54cc9d76123a
13 files changed