When tiled rendering, then only the render context (or failing that,
SwViewShell::GetOut()) has the correct zoom level, so use that when
doing pixel-to-logic conversion or scaling pixel values.

Change-Id: I265a642b8253c6eced42da2a0e06a2de25c36ca8
(cherry picked from commit 8a249d38e94098b300fb4f49cb4a44960027fa20)