update header sending status in-place (more so)

Previously, an in-place header update avoided a WebView
re-render, but did re-render all overlays. This is normally
imperceptible, but thumbnail views flicker as they are rendered.

Since only a couple of overlay views are truly affected by
sender updates, update those views in-place when they are
present. This is only supported on MessageHeaderViews for now.

Bug: 7434748
Change-Id: Ifdebea1410dadfceefae52d406891b5383e9ab15
5 files changed