[vr] Determine reticle position based on mouse position in test app

With this change, we convert the current mouse position into a ray that
we use for an initial hit test. Based on the result of that hit test,
we construct a controller position and orientation so that it points at
the reticle.

Bug: None
Change-Id: I584f9963b6fe37dda9806d0833a2183a677f77be
Reviewed-on: https://chromium-review.googlesource.com/754543
Reviewed-by: Christopher Grant <cjgrant@chromium.org>
Commit-Queue: Ian Vollick <vollick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#514298}
4 files changed