Extend SurfaceToolbar into TargetToolbar

Toolbars may want to control the target as well as the surface (spoiler alert!).
The new TargetToolbar has a pointer to its target as well as its surface.

Change-Id: I928316d9e23ac3f3de3e76c34ef0ac3d27855ab3
Merge "Extend SurfaceToolbar into TargetToolbar"