Add mechanism to use offscreen for context views.

Added mechanism to use offscreen rendering for context views. This also add
support to capture images without offscreen for context views. Thus context
views now behave similar to render views for capturing screenshots and offscreen
rendering.

Change-Id: I5b42f504cd7a2bec14406bec36b52bd5d468f215
Merge topic '14280_fix_multiview_rendering_in_batch' into next

a9a3b90 Add mechanism to use offscreen for context views.